Hi, I have been looking for a bunch of 12AV7's to replace the 12AY7's in a couple guitar amps.
12AV7's appear to be very close to the 12AY7's but I might be missing the bottom line on compatability.
I have a couple sylvania branded tubes which seem like a near perfect match in the amp.
Does anyone have any experience with GE branded 5965? It is my understanding it might also be a viable replacement for the 12AV7.
Trout
12AV7's appear to be very close to the 12AY7's but I might be missing the bottom line on compatability.
I have a couple sylvania branded tubes which seem like a near perfect match in the amp.
Does anyone have any experience with GE branded 5965? It is my understanding it might also be a viable replacement for the 12AV7.
Trout
I'm interested in this topic too, but I'm on your side of the field, asking if:
Take a look at this site, and look at the description for the "classic" 5F6A.
http://www.thetubestore.com/earfenam.html#tweed Bassman 5F6A
They say that "not" using a 12AY7 will change the sound, and they recommend, if not a 12AY7, to use a 6072A. (which is expensive)
They also say not to use a 5U4 or other than a GZ34. Why?
I've finally amassed several 5U4's since I have has the best of luck with them on my hi-fi amps.
The 5F6A has 4 input jacks, 2 for bright and 2 for normal.
On mods I've seen, they use a 12AX7 for the input stage, instead of the 12AY7, and then still 2 more 12AX7's for the second pre-amp stage (pre-tone block/phase inverter) and then the driver stage to the finals.
Only the first tube is different, it's used as a series gain, instead of a 4 channel parallel.
I found this mod a few months back, I couldn't find it today, as this gent rearranged his pages and it came up 404, but I did scan it from my paper copy:
Click on the link:
http://viewoftheblue.com/tubeworks/out.jpg
(I used a highlighter over all the pots switches & controls, so that's my work, and I hope you can see the gist of the circuit in spite of this marking)
Take a look at this site, and look at the description for the "classic" 5F6A.
http://www.thetubestore.com/earfenam.html#tweed Bassman 5F6A
They say that "not" using a 12AY7 will change the sound, and they recommend, if not a 12AY7, to use a 6072A. (which is expensive)
They also say not to use a 5U4 or other than a GZ34. Why?
I've finally amassed several 5U4's since I have has the best of luck with them on my hi-fi amps.
The 5F6A has 4 input jacks, 2 for bright and 2 for normal.
On mods I've seen, they use a 12AX7 for the input stage, instead of the 12AY7, and then still 2 more 12AX7's for the second pre-amp stage (pre-tone block/phase inverter) and then the driver stage to the finals.
Only the first tube is different, it's used as a series gain, instead of a 4 channel parallel.
I found this mod a few months back, I couldn't find it today, as this gent rearranged his pages and it came up 404, but I did scan it from my paper copy:
Click on the link:
http://viewoftheblue.com/tubeworks/out.jpg
(I used a highlighter over all the pots switches & controls, so that's my work, and I hope you can see the gist of the circuit in spite of this marking)
Now to go a few steps further. I would like to use a 5U4GB or GC in the power supply, any problem with that? I would eliminate the diodes and use tried & true capicitors 47uF / 100uF and a good min 7H choke.
As for questions on this circuit: I see they have 2 differing inputs, and 2 resistors stacked for them, which would be best for guitar and/or mic/other and why?
There's also an "early" volume control between stages of the first tube, then a master after the second tube and the tone stack. Any comments on this design?
The "smooth switch" circuit and it's 3 components (the 22M 10M and .047uf cap are entirely optional according to the author and can be omitted)
Then there's a bunch of stuff like the gain switch, deep switch, and half power switch.
Also a "presence" just before the last stage before the finals.
And also a fine-tune bias adj in the power supply area.
Aside from these mods, and looking at the original Bassman (which uses 5881's, and here using 6L6GC's), does this look like (in its entirety) that with the components shown here on the finals, (220k + 1500k to the triode grids from -48.7v)
and 438 B+ to 1k resistors for the tetrode grids
and 439 vdc through the OPT to the plates would work fine?
Just saying that because this guy has revised and moved his schematics quite a bit, and I'm hoping this would all look to be in the correct ballpark from a good observer, as I'd like to build one of these myself, and am ready to order the parts.
Thanks.
As for questions on this circuit: I see they have 2 differing inputs, and 2 resistors stacked for them, which would be best for guitar and/or mic/other and why?
There's also an "early" volume control between stages of the first tube, then a master after the second tube and the tone stack. Any comments on this design?
The "smooth switch" circuit and it's 3 components (the 22M 10M and .047uf cap are entirely optional according to the author and can be omitted)
Then there's a bunch of stuff like the gain switch, deep switch, and half power switch.
Also a "presence" just before the last stage before the finals.
And also a fine-tune bias adj in the power supply area.
Aside from these mods, and looking at the original Bassman (which uses 5881's, and here using 6L6GC's), does this look like (in its entirety) that with the components shown here on the finals, (220k + 1500k to the triode grids from -48.7v)
and 438 B+ to 1k resistors for the tetrode grids
and 439 vdc through the OPT to the plates would work fine?
Just saying that because this guy has revised and moved his schematics quite a bit, and I'm hoping this would all look to be in the correct ballpark from a good observer, as I'd like to build one of these myself, and am ready to order the parts.
Thanks.
Both of The Models I tinker with call for 12AY7's in the v1 position.
Up until recently I had just used 12AX7's. In my 5E7 thats great, it had no adverse effects, But my 5E3's tend to be far to raw and gritty. Like a runaway frieght train.
I had a few 12AV7's laying around and figured eh, Try them, It cant hurt.
Well, in the 5E3 Deluxe it is a huge improvement. Smoother overdriven tones, and a much more linear volume control.
There are not many new prodution 12AY7's around, EH makes one, And Groove tubes sells some relabeled version.
So looking at NOS was an eye opener, 12AY7's average around 35.00 each on ebay?
OUCH!
12AV7's average $2.50? Thats pretty darn sensible.
I found a bulk lot of 5965 at a bargain, But Im confused on this one.
The Data sheet says computer tubes but this sheets says see 12AV7. http://www.nj7p.org/Tube4.php?tube=5965
Trout
Up until recently I had just used 12AX7's. In my 5E7 thats great, it had no adverse effects, But my 5E3's tend to be far to raw and gritty. Like a runaway frieght train.
I had a few 12AV7's laying around and figured eh, Try them, It cant hurt.
Well, in the 5E3 Deluxe it is a huge improvement. Smoother overdriven tones, and a much more linear volume control.
There are not many new prodution 12AY7's around, EH makes one, And Groove tubes sells some relabeled version.
So looking at NOS was an eye opener, 12AY7's average around 35.00 each on ebay?
OUCH!
12AV7's average $2.50? Thats pretty darn sensible.
I found a bulk lot of 5965 at a bargain, But Im confused on this one.
The Data sheet says computer tubes but this sheets says see 12AV7. http://www.nj7p.org/Tube4.php?tube=5965
Trout
hi Trout,
U had perfect eye sight of tubes.
Since the sepc of 6072/12ay7 will close to 12ax7 but had different pins out.
If U like the 5965, pls considerate keep 7062/E180cc, this was HQ versions of 5965 & telefunken 5965 also a good choice.
I had bulk of this tube for future diy project use.
thx
thomas
U had perfect eye sight of tubes.
Since the sepc of 6072/12ay7 will close to 12ax7 but had different pins out.
If U like the 5965, pls considerate keep 7062/E180cc, this was HQ versions of 5965 & telefunken 5965 also a good choice.
I had bulk of this tube for future diy project use.
thx
thomas
Wow, lots of things to clear up here, let me see if I can be of any help...
1. The 12AV7 has similar mu to a 12AY7/6072, but is tonally somewhat different. It does draw 50% more heater current than a 12AY7, but for most amps it's no problem if you are swapping one tube.
The GE clear top 5965 is a terrific tube in the 12AV7 family, but they can be a bit microphonic. Another 12AV7 family tube is the 7062/E180CC, it's quite nice but pricier. The 12AV7 is a steal!
2. The 5U4 family draws an amp more heater current than the 5AR4. Some amps can supply that, some can't. That's why it's recommended that you not use it.
3. There is no such thing as a 5U4GC (unless it's a relabel of some sort by a vendor). There was the 5U4G "coke" bottle, the 5U4GA, and the 5U4GB - and it's "twin", the 5AS4.
4. The fact that the data sheet says "computer tube" means NOTHING! Most tubes used in audio or music amps were originally designed for something else. A "computer tube" usually has a cathode that is specially constructed to resist "poisoning" (a lack of emissions) after being off for a long period as you might find in a logic gate in a computer. That's it.
5. You can replace the diodes with a tube rectifier, but it won't be easy. You need heater power and an appropriate secondary configuration for a tube. The SS diodes didn't have the same needs.
6. The 6072 and 12AY7 pinout is identical to the 12AX7.
1. The 12AV7 has similar mu to a 12AY7/6072, but is tonally somewhat different. It does draw 50% more heater current than a 12AY7, but for most amps it's no problem if you are swapping one tube.
The GE clear top 5965 is a terrific tube in the 12AV7 family, but they can be a bit microphonic. Another 12AV7 family tube is the 7062/E180CC, it's quite nice but pricier. The 12AV7 is a steal!
2. The 5U4 family draws an amp more heater current than the 5AR4. Some amps can supply that, some can't. That's why it's recommended that you not use it.
3. There is no such thing as a 5U4GC (unless it's a relabel of some sort by a vendor). There was the 5U4G "coke" bottle, the 5U4GA, and the 5U4GB - and it's "twin", the 5AS4.
4. The fact that the data sheet says "computer tube" means NOTHING! Most tubes used in audio or music amps were originally designed for something else. A "computer tube" usually has a cathode that is specially constructed to resist "poisoning" (a lack of emissions) after being off for a long period as you might find in a logic gate in a computer. That's it.
5. You can replace the diodes with a tube rectifier, but it won't be easy. You need heater power and an appropriate secondary configuration for a tube. The SS diodes didn't have the same needs.
6. The 6072 and 12AY7 pinout is identical to the 12AX7.
Thanks
for the 12AV7 info Jim!
I have both RCA, and Sylvania 12AV7's here I have been testing in a 5E3 combo and have not run into any microphonic symptoms yet. At the current NOS price t looks to be a good viable replacement for the 12AY7.
The 5965 seems to be really plentiful also, In fact more so than the 12AV7.
My question is does anyone know what brand 5965 to avoid? I see loads of GE's out there.
Trout
for the 12AV7 info Jim!
I have both RCA, and Sylvania 12AV7's here I have been testing in a 5E3 combo and have not run into any microphonic symptoms yet. At the current NOS price t looks to be a good viable replacement for the 12AY7.
The 5965 seems to be really plentiful also, In fact more so than the 12AV7.
My question is does anyone know what brand 5965 to avoid? I see loads of GE's out there.
Trout
Thanks for the replies, Jim especially, hopefully I'll be making a new 5F6A clone soon, and this thread has provided some vital info.
I see the pinouts for the 12AY7, 12AV7 and 12AX7 are identical, as are the heater amp ratings (.3a), but the 12AV7 uses .45a
Sounds great that the 12AV7's have given you (Trout) good luck as far as microphonics go, they may be a good route in that case, especially with the price of NOS being great.
There is a 5U4GC, I bought one and it's a Ruby (Russian, I believe), and has the old wavy "G" profile, I assume it's the same spec as a GB. Probably one brand's way to say it "newer".
As far as using a tube rectifier rather than a solid state, I'm trying to go with the original specs, and I'll be drilling the chassis, not converting a unit.
The power xfmr called for is this one:
http://www.tubesandmore.com/scripts...vclients/cemirror/ELEVATOR.FXP?item=P-TF22798
This does provide enough current (3amps) for a 5U4GB, but from what I've read, the time curves of a GZ34 (going from zero sound to some heavy playing) react well with this amp to provide the best response curves, so that should probably be the way to go.
So for me the original 5F6A plan seems the best, but there are a few mods I'm tempted to try (opinions please):
1) Using a 12AX7 as the input tube, cutting down the 4 input jacks to two, and having an extra gain stage, in conjunction with putting a "bright" switch in the cathode circuit of the very first tube element
2) A "deep switch" above the tone stack, and a "master" just after, would this keep the response and distortion fairly the same at a lower power level (cutting down the volume and keeping the same effects) , or is it not really worth adding?
The one mod also adds a half power switch.
3) A bias adjustment pot 10k, for 6L6GC's, or is the standard 48v in the original circuit OK, given the chance of some minor fluctuation?
I see the pinouts for the 12AY7, 12AV7 and 12AX7 are identical, as are the heater amp ratings (.3a), but the 12AV7 uses .45a
Sounds great that the 12AV7's have given you (Trout) good luck as far as microphonics go, they may be a good route in that case, especially with the price of NOS being great.
There is a 5U4GC, I bought one and it's a Ruby (Russian, I believe), and has the old wavy "G" profile, I assume it's the same spec as a GB. Probably one brand's way to say it "newer".
As far as using a tube rectifier rather than a solid state, I'm trying to go with the original specs, and I'll be drilling the chassis, not converting a unit.
The power xfmr called for is this one:
http://www.tubesandmore.com/scripts...vclients/cemirror/ELEVATOR.FXP?item=P-TF22798
This does provide enough current (3amps) for a 5U4GB, but from what I've read, the time curves of a GZ34 (going from zero sound to some heavy playing) react well with this amp to provide the best response curves, so that should probably be the way to go.
So for me the original 5F6A plan seems the best, but there are a few mods I'm tempted to try (opinions please):
1) Using a 12AX7 as the input tube, cutting down the 4 input jacks to two, and having an extra gain stage, in conjunction with putting a "bright" switch in the cathode circuit of the very first tube element
2) A "deep switch" above the tone stack, and a "master" just after, would this keep the response and distortion fairly the same at a lower power level (cutting down the volume and keeping the same effects) , or is it not really worth adding?
The one mod also adds a half power switch.
3) A bias adjustment pot 10k, for 6L6GC's, or is the standard 48v in the original circuit OK, given the chance of some minor fluctuation?
OK, I show the 5F6A as being a 1958-1960 Tweed Bassman correct?
http://www.ampwares.com/ffg/bassman_narrow.html
I personally use that exact transformer on a couple of 1957 5E7 Bandmasters I have built. It is rock solid and has a plenty stiff feel in the bass department even in a guitar amp.
The 5E7 utilized a 5U4GB rectifier. In fact, there are very few differences in the schematics.
This would be the correct output transformer also.
P-TF22855
Replacement for Tweed Bassman, Super Reverb, and Concert amps, 2 ohms. Equivalent to #125A9A & #022855
I however have been using this unit for a bit more flexibility as far as speaker cabs got.
P-TF18343
General replacement 2/4/8 ohm transformer, can be used on many 50 watt amps. Equivalent to #125A13A & #018343.
The Trick here being I use the bigger bassman transformers in my 5E7. I also added the 10K bias pot to allow more accurate bias adjustment.
Original 5E7 Schematic http://www.ampwares.com/ffg/schem/bandmaster_5e7_schem.gif
As far as the bassman goes, I think I would stick pretty close to the original schematic. It is really easy to locate turret or eyelet boards for it and it does sound fantastic.
For guitar I still like the modded 5E7 best.
Trout
Thanks Trout, that's an excellent suggestion for the OPT, your idea does support more configs rather than just the 2 ohms (series speakers etc).
According to some research I've done, the negative feedback was originally sent from the 2 ohm tap with a 27k resistor, more commonly now on clones I believe they are using the 4 ohm tap and a 56k resistor.
I may still go with a GZ34 for authenticity, but the jury's still out.
I just noticed that Weber makes a 5F6A kit for $650, I'm going to do mine by hand, but the interesting part is that they have a redrawn schematic of the 5F6A, all the components are exactly the same as far as I can tell, but they do use a 12AX7 for the first tube rather than a 12AY7, and also show how to put in a bias pot. They show a "WZ34" (I probably won't use this method)
instead of a tube rectifier for $26 (and BTW both tubesandmore & Angela also offer versions of these).
http://www.thetubestore.com/wb-wz34.html
Here's the Weber redrawn schematic:
http://www.weberspeakers.com/store/5f6a_schem.jpg
And along my travels I saw one guy's nice work on a chassis:
http://home.comcast.net/~bckellett/5F6A.jpg
But I'm going to use a wider chassis and mount the tubes on the top instead of upside down, use point-to-point wiring rather than a board, and eventually build a "head" cabinet accordingly.
So unless there are any other mods I mentioned above that are almost indispensible, I guess I have the ideas pretty much worked out now at this point. Appreciated your ideas, thanks..
One thing I should ask though, I see some people putting a shield around one of the 12AX7's, sometimes all three, since this may shorten tube life due to heat, where is this really neccessary or recommended? The very first tube?
According to some research I've done, the negative feedback was originally sent from the 2 ohm tap with a 27k resistor, more commonly now on clones I believe they are using the 4 ohm tap and a 56k resistor.
I may still go with a GZ34 for authenticity, but the jury's still out.
I just noticed that Weber makes a 5F6A kit for $650, I'm going to do mine by hand, but the interesting part is that they have a redrawn schematic of the 5F6A, all the components are exactly the same as far as I can tell, but they do use a 12AX7 for the first tube rather than a 12AY7, and also show how to put in a bias pot. They show a "WZ34" (I probably won't use this method)
instead of a tube rectifier for $26 (and BTW both tubesandmore & Angela also offer versions of these).
http://www.thetubestore.com/wb-wz34.html
Here's the Weber redrawn schematic:
http://www.weberspeakers.com/store/5f6a_schem.jpg
And along my travels I saw one guy's nice work on a chassis:
http://home.comcast.net/~bckellett/5F6A.jpg
But I'm going to use a wider chassis and mount the tubes on the top instead of upside down, use point-to-point wiring rather than a board, and eventually build a "head" cabinet accordingly.
So unless there are any other mods I mentioned above that are almost indispensible, I guess I have the ideas pretty much worked out now at this point. Appreciated your ideas, thanks..
One thing I should ask though, I see some people putting a shield around one of the 12AX7's, sometimes all three, since this may shorten tube life due to heat, where is this really neccessary or recommended? The very first tube?
Hi Frank,
I only use the shields to protect the tubes, In some high gain amps putting the shield on V1 seems to be important as they tend to get a lot of noise.
Here is a few pictures of a 5E7 Bandmaster chassis I prototyped a while back. I have since made a few more refinements but basically this is pretty much what I did. This was pretty much a totally from scratch project.
Bandmaster Chassis
I added a post PI master volume, and midrange control as well as adding the bias pot. I also ended up needing screen resistors.
I get just enough range out of the bias pot to run anything from 6L6GC, to KT77's.
It is incredibly loud, Has outstanding clean tones, Vicious complex overdriven tone when the volume is pushed up. I can keep it well below ear bleed levels rolling back the master volume.
I have nice laser engraved plexi faceplates from BNP laser in PA and mounted it up in a tweed 2 X 12 Cab.
As far as running a 12AX7 in the V1 position, I do it all the time, but just recently I have been playing with tubes offering a bit less gain in V1. I think Leo was really on to something there.
If I were you, I would think about grabbing a couple 12AV7's or 12AY7's just to try. I really like the tonal improvement.
But, either way, Sounds like your off to a good start.
Trout
I only use the shields to protect the tubes, In some high gain amps putting the shield on V1 seems to be important as they tend to get a lot of noise.
Here is a few pictures of a 5E7 Bandmaster chassis I prototyped a while back. I have since made a few more refinements but basically this is pretty much what I did. This was pretty much a totally from scratch project.
Bandmaster Chassis
I added a post PI master volume, and midrange control as well as adding the bias pot. I also ended up needing screen resistors.
I get just enough range out of the bias pot to run anything from 6L6GC, to KT77's.
It is incredibly loud, Has outstanding clean tones, Vicious complex overdriven tone when the volume is pushed up. I can keep it well below ear bleed levels rolling back the master volume.
I have nice laser engraved plexi faceplates from BNP laser in PA and mounted it up in a tweed 2 X 12 Cab.
As far as running a 12AX7 in the V1 position, I do it all the time, but just recently I have been playing with tubes offering a bit less gain in V1. I think Leo was really on to something there.
If I were you, I would think about grabbing a couple 12AV7's or 12AY7's just to try. I really like the tonal improvement.
But, either way, Sounds like your off to a good start.
Trout
Nice pix Trout, looks like that was a great project.
I guess I'll get the shields, the little tubes always seem to get pushed around a bit while working with them left in.
I will also order a 12AV7 too see the difference once I try it out.
I'm also thinking of adding a "master" pot, can't really go wrong with this, as it adds an extra feature.
On most of these DIY remakes, with 2-4 speaker jacks, do most people want them to be 4 ohm or 8 ohm?
I see the Weber schematic putting up to 4 speakers in parallel.
I was thinking of just 2 speaker jacks, from the 8 ohm tap, with a switch for 8 or 4 ohms, depending on if 1 or 2 speakers were plugged in. And I'm also assuming the 56k feedback resistor is hardwored to the 4 ohm terminal of the OPT.
Well, appreciate the tips & encouragement, we'll see how this turns out, in a couple of weeks or so...
I guess I'll get the shields, the little tubes always seem to get pushed around a bit while working with them left in.
I will also order a 12AV7 too see the difference once I try it out.
I'm also thinking of adding a "master" pot, can't really go wrong with this, as it adds an extra feature.
On most of these DIY remakes, with 2-4 speaker jacks, do most people want them to be 4 ohm or 8 ohm?
I see the Weber schematic putting up to 4 speakers in parallel.
I was thinking of just 2 speaker jacks, from the 8 ohm tap, with a switch for 8 or 4 ohms, depending on if 1 or 2 speakers were plugged in. And I'm also assuming the 56k feedback resistor is hardwored to the 4 ohm terminal of the OPT.
Well, appreciate the tips & encouragement, we'll see how this turns out, in a couple of weeks or so...
frank754 said:
On most of these DIY remakes, with 2-4 speaker jacks, do most people want them to be 4 ohm or 8 ohm?
I see the Weber schematic putting up to 4 speakers in parallel.
I was thinking of just 2 speaker jacks, from the 8 ohm tap, with a switch for 8 or 4 ohms, depending on if 1 or 2 speakers were plugged in. And I'm also assuming the 56k feedback resistor is hardwored to the 4 ohm terminal of the OPT.
Well, appreciate the tips & encouragement, we'll see how this turns out, in a couple of weeks or so...
IMO, anything over 1 extra speaker jacks is just chassis drilling practice and really offers no advantages.
On Combo style amps I never put the extra jacks, and generally leave out the impedance selector switch. I hard wire the jack for 8 ohms.
I always fear that someone will upset the impedance and overload and fry the OT or output tubes.
The amp in the pictures is a combo amp with 2-12" 16 ohm speakers wired to 8 Ohm.
Unlike the good ole days when we needed 100-150W, Generally speaking anything over 40W is just about overkill for most small venues. These days everything gets Mic'd and mixed down through the PA.
Most local guys out this way use 1 or 2-12" combo amps.
We all at the mercy of the sound engineer
The last gig that I used my 50W, A bar on New Years Eve, crowd of maybe 120 people, My amp never left "2" on the volume control!
Sad to, because when ever we want to push over the edge to get the best sound it needs to be on "11"
Another Spinal Tap moment!
As far as the 56K feedback resistor, I always tap off the highest ohm possible on the OT.
I had run into some weird oscillation issues on the lower taps that I never did figure out.
I grabbed up a bunch of NOS 12AV7's on ebay yesterday, I like keeping a good stockpile whenever possible. I got RCA's Sylvanias and also got a dozen 5965GE's.
Soon as they get here I'll post which brand I like best.
Trout
Cool, that definitely makes sense, wiring for 8 ohms to be safe.
I have a 1/4" plugin 12" vintage 8 ohm repro Jensen Alnico speaker to test this out with. For my tube hi-fi mono gear I have a pair of new Audio Nirvana super 10's in parallel at 4 ohms. I will test it out on both platforms for sound, and use the OPT taps for testing.
As you say though, probably best to just do a single 8 ohm output, so they will be responsible if they fry anything.
I'm not going to sell my prototype, but I do know a few guys in one band that are eventually starting an online store, and will use me to make this stuff if it ever comes to be, so my thinking is in that case for the end user.
I ordered all the parts, it's about $400. Sure hope my taxes next month don't kick me in the butt as well.
From the site pentodepress.com/summary.html they make an important observation of the final power stage:
QUOTE:
The Marshall JTM45 power amp is a direct copy of the Bassman 5F6A circuit except for one very important change: the negative feedback signal is taken from the 16-ohm transformer output instead of the 2-ohm output. This almost triples the feedback voltage, which reduces nonlinear distortion and flattens the amplifier's frequency response at the cost of less overall gain. Later Marshalls, including the JMP50 Model 1987, use EL34 pentodes, so although the push-pull, class AB circuit design is the same (except for component values and supply voltages), the tube change dramatically alters its characteristics.
So I would say since the original Bassman used 27k from the 2 ohm tap, the later copies used 56k from the 4 ohm, but I guess that's just a wait & see performance test that I can experimant with at that point to see how it sounds.
Anyway, maybe early next week the parts will arrive, and I have most of the week off, so should be fun
I have a 1/4" plugin 12" vintage 8 ohm repro Jensen Alnico speaker to test this out with. For my tube hi-fi mono gear I have a pair of new Audio Nirvana super 10's in parallel at 4 ohms. I will test it out on both platforms for sound, and use the OPT taps for testing.
As you say though, probably best to just do a single 8 ohm output, so they will be responsible if they fry anything.
I'm not going to sell my prototype, but I do know a few guys in one band that are eventually starting an online store, and will use me to make this stuff if it ever comes to be, so my thinking is in that case for the end user.
I ordered all the parts, it's about $400. Sure hope my taxes next month don't kick me in the butt as well.
From the site pentodepress.com/summary.html they make an important observation of the final power stage:
QUOTE:
The Marshall JTM45 power amp is a direct copy of the Bassman 5F6A circuit except for one very important change: the negative feedback signal is taken from the 16-ohm transformer output instead of the 2-ohm output. This almost triples the feedback voltage, which reduces nonlinear distortion and flattens the amplifier's frequency response at the cost of less overall gain. Later Marshalls, including the JMP50 Model 1987, use EL34 pentodes, so although the push-pull, class AB circuit design is the same (except for component values and supply voltages), the tube change dramatically alters its characteristics.
So I would say since the original Bassman used 27k from the 2 ohm tap, the later copies used 56k from the 4 ohm, but I guess that's just a wait & see performance test that I can experimant with at that point to see how it sounds.
Anyway, maybe early next week the parts will arrive, and I have most of the week off, so should be fun
Take lots of pictures during the build!!
I am finding that often just reviewing my own work via photographs helps me improve my build quality.
Several times during a build I looked at the pictures and was actually stunned by a couple of outright silly mistakes!
Silly things like un-soldred ground wire, wrong resistor, and pot wiring mistake.
Sure beats troubleshooting later.
Trout
I am finding that often just reviewing my own work via photographs helps me improve my build quality.
Several times during a build I looked at the pictures and was actually stunned by a couple of outright silly mistakes!
Silly things like un-soldred ground wire, wrong resistor, and pot wiring mistake.
Sure beats troubleshooting later.
Trout
Well I got the parts today, and so far got it drilled and the hardware placed, but not all tightened down.
On the front there will be, power, standby, pilot light, presence, middle, bass, treble, master, bright vol, normal vol, and 4 jacks.
The back has the hole for the power cord, the fuse, and two 8 ohm speaker jacks in the middle.
On the underside, I routed the OPT leads to the left to be closest to where they need to be, and far from the pre-amp areas.
The GZ34 will be farthest to the left. With such a good-sized chassis I can put the 4 huge Sprague 20uF 600v caps under by the power tranny. That will leave part of the top empty.
Tomorrow I'm off and it will be a long day...
On the front there will be, power, standby, pilot light, presence, middle, bass, treble, master, bright vol, normal vol, and 4 jacks.
The back has the hole for the power cord, the fuse, and two 8 ohm speaker jacks in the middle.
On the underside, I routed the OPT leads to the left to be closest to where they need to be, and far from the pre-amp areas.
The GZ34 will be farthest to the left. With such a good-sized chassis I can put the 4 huge Sprague 20uF 600v caps under by the power tranny. That will leave part of the top empty.
Tomorrow I'm off and it will be a long day...
Wow, Those are some huge caps!!
Looks like your off to a really good start!
When I did my head version in a Hammond chassis, My layout was way different, But I opted for a eyelet board with smaller caps on the board.
I used a heavy copper buss ground and located everything as close as practical to keep wire lengths down. I only put in 2 input jacks though looking back I did have room for the other 2.
This one had Standby, Power Switch, Presence, Bass, Treble, Master Volume, and Volume 1 & 2.
Same PT and OT. I dropped the choke and just used a resistor instead. 5U4 rectifier.
I mounted a Marshall selector switch on the back for output impedance 2-4 & 8 ohm.
This chassis is still in daily use over at my brothers.
Trout
Looks like your off to a really good start!
When I did my head version in a Hammond chassis, My layout was way different, But I opted for a eyelet board with smaller caps on the board.
I used a heavy copper buss ground and located everything as close as practical to keep wire lengths down. I only put in 2 input jacks though looking back I did have room for the other 2.
This one had Standby, Power Switch, Presence, Bass, Treble, Master Volume, and Volume 1 & 2.
Same PT and OT. I dropped the choke and just used a resistor instead. 5U4 rectifier.
I mounted a Marshall selector switch on the back for output impedance 2-4 & 8 ohm.
This chassis is still in daily use over at my brothers.
An externally hosted image should be here but it was not working when we last tested it.
Trout
Well, I got it going. I spent 14 hours yesterday wiring the beast after the driiling and mounting the day before, and then 4 hours this morning triple-checking everything, and doing some minor cosmetic tweaks, etc.
I always check all the resistors with my ohmmeter, and other parts as well in case I overheated any by soldering.
Didn't find any mistakes, so I ran it with just the rectifier, adjusted the bias, checked voltages, etc.
Then cranked it up with a cheap electric guitar I have (I'm not a musician), and a microphone. Seems to work fine, all controls do what they are supposed to. Put on the decals made with a labeler.
It's an exact clone of the 5F6-A except for these tweaks:
I used the 8 ohm OPT tap (the other leads are strapped in a neat bundle on the center of the underside for eventual experimentation). With 2 speakers plugged it would become 4 ohms, which is ok.
56K feedback resistor from the 8 ohm tap
Added a bias pot (the original schematic says -48 volts, so that's what I have it set at). Added a "master" volume, the black knob, as you can only get the cream knobs in 6's. Makes it stand out.
3-wire power cord and no "ground" switch needed.
Used a 12AX7 instead of a 12AY7 for the first stage, bought a 12AV7 to try at some point.
It has two matched TAD black-plate 6L6GC-STR tubes, three JJ ECC83's, and a Ruby 5AR4. All carbon comp resistors in the signal path, and all Switchcraft jacks, Alpha pots and ceramic tube sockets.
I used point to point wiring and terminal strips, but there are only a few chassis ground points, one for each stage (or less). On the control & input jack areas, I wired all the pot fins which needed to be grounded in a loop, as well as all the jack ground lugs, and ran these to chassis ground as well in case they ever come loose it won't be a problem, everything's wrenched very tightly anway. I put silicone under the big caps so they won't budge either, and heat shrink tubing on some of the orange capacitor leads to protect them where someone could possibly push the leads to a ground point and short them (I kept them fairly short & tight as is though).
Also tried to put most of the components associated with the controls up in that area, greatly reducing potential clutter around the tube sockets.
So basically it seems like a success, will have to run it by an expert musician to get a good opinion though, one of these days.
Tomorrow I'm going to start working on a head cabinet, the weather is a bit warmer the last few days, finally.
Thanks for your interest.
I always check all the resistors with my ohmmeter, and other parts as well in case I overheated any by soldering.
Didn't find any mistakes, so I ran it with just the rectifier, adjusted the bias, checked voltages, etc.
Then cranked it up with a cheap electric guitar I have (I'm not a musician), and a microphone. Seems to work fine, all controls do what they are supposed to. Put on the decals made with a labeler.
It's an exact clone of the 5F6-A except for these tweaks:
I used the 8 ohm OPT tap (the other leads are strapped in a neat bundle on the center of the underside for eventual experimentation). With 2 speakers plugged it would become 4 ohms, which is ok.
56K feedback resistor from the 8 ohm tap
Added a bias pot (the original schematic says -48 volts, so that's what I have it set at). Added a "master" volume, the black knob, as you can only get the cream knobs in 6's. Makes it stand out.
3-wire power cord and no "ground" switch needed.
Used a 12AX7 instead of a 12AY7 for the first stage, bought a 12AV7 to try at some point.
It has two matched TAD black-plate 6L6GC-STR tubes, three JJ ECC83's, and a Ruby 5AR4. All carbon comp resistors in the signal path, and all Switchcraft jacks, Alpha pots and ceramic tube sockets.
I used point to point wiring and terminal strips, but there are only a few chassis ground points, one for each stage (or less). On the control & input jack areas, I wired all the pot fins which needed to be grounded in a loop, as well as all the jack ground lugs, and ran these to chassis ground as well in case they ever come loose it won't be a problem, everything's wrenched very tightly anway. I put silicone under the big caps so they won't budge either, and heat shrink tubing on some of the orange capacitor leads to protect them where someone could possibly push the leads to a ground point and short them (I kept them fairly short & tight as is though).
Also tried to put most of the components associated with the controls up in that area, greatly reducing potential clutter around the tube sockets.
So basically it seems like a success, will have to run it by an expert musician to get a good opinion though, one of these days.
Tomorrow I'm going to start working on a head cabinet, the weather is a bit warmer the last few days, finally.
Thanks for your interest.
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