Hi Guys,
Basically, I am in the process of sorting out a homebrew guitar amp.
I have a question about replacing the choke with a simple resistor. Right now, I have the unit built, But my voltages are low after the replaced part. I have no specs on what the original design used as far as a choke, Several places sell a universial unit that is 5-8H @ 200ma, 125 ohms.
What value resistor would be approximately the correct Value?
The original PS Was as Follows,
16UF->Choke->16UF->10K5W->16UF->10K1W->8UF-> to preamp
Back when this circuit was produced 1950's, I figured they needed better filtering with those caps.
I have the unit set up as follows
30UF->10K10W->30UF->10K5W->30UF->10K1W->16UF-> to preamp.
The voltage drop is way off spec, more than 100V!!
I suspect the resistor should be around 125ohm 10W?
Trout
Basically, I am in the process of sorting out a homebrew guitar amp.
I have a question about replacing the choke with a simple resistor. Right now, I have the unit built, But my voltages are low after the replaced part. I have no specs on what the original design used as far as a choke, Several places sell a universial unit that is 5-8H @ 200ma, 125 ohms.
What value resistor would be approximately the correct Value?
The original PS Was as Follows,
16UF->Choke->16UF->10K5W->16UF->10K1W->8UF-> to preamp
Back when this circuit was produced 1950's, I figured they needed better filtering with those caps.
I have the unit set up as follows
30UF->10K10W->30UF->10K5W->30UF->10K1W->16UF-> to preamp.
The voltage drop is way off spec, more than 100V!!
I suspect the resistor should be around 125ohm 10W?
Trout
OHHHHhhhhhhhh YESSSSSSSSSSSS
Swapped out the 10K-10W to a 130-10W and everything hits about perfect. 405V at the plates, and -37V bias never sounded so good!!
I finally found an opt I like, I like A LOT! Rated for 50W this thing sounds like a million bucks. Tightest bass I have ever gotten, Yet the high end sparkles. My good American Strat is at my brothers for some video soundtrack job he is recording, So I have my daughters 150.00 fender squire plugged in, Oddly, It sounds as good as a $4000 Gretsch with the clean Jazz type settings!
Only thing I never thought about was now that its this loud, I need ear muffs to get into the heavily overdriven tones lol
Perhaps a few tweaks on one of the preamp channels will bring that back a little.
Now its time to roll a few tubes, I am dying to try the JJ KT77's out lol
Trout
Swapped out the 10K-10W to a 130-10W and everything hits about perfect. 405V at the plates, and -37V bias never sounded so good!!
I finally found an opt I like, I like A LOT! Rated for 50W this thing sounds like a million bucks. Tightest bass I have ever gotten, Yet the high end sparkles. My good American Strat is at my brothers for some video soundtrack job he is recording, So I have my daughters 150.00 fender squire plugged in, Oddly, It sounds as good as a $4000 Gretsch with the clean Jazz type settings!
Only thing I never thought about was now that its this loud, I need ear muffs to get into the heavily overdriven tones lol
Perhaps a few tweaks on one of the preamp channels will bring that back a little.
Now its time to roll a few tubes, I am dying to try the JJ KT77's out lol
Trout
maxwedge said:
An old 1955 Fender Bandmaster 5E7 with a beefed up output stage.
I have built a few 5D4 Supers with a 5E7 front end prior to this one, but that did not use a choke at all on the original 5D4.
I got a great deal on a few 5E7 compatable power transformers and wanted to go to an adjustable fixed bias since the PT had the proper 50V tap.
I may have spoke to soon though on this fix. I just experienced the classic " To much capacitance" symptom Internal Rectifier Tube Arc . I am guessing that 30uf on the first cap is excessive when combined with only 130R and another 30UF.
Right now I am as follows
5U4->30UF->130-10W->30UF->10K5W->30UF->10K1W->16UF-> to preamp.
It behaves like it is seeing way more than 30uf so most likely I will need to lower the first cap to 16UF.
It arced once when I flipped on the standby switch, I replaced the tube(just in case)
Played about 30 minutes and got another arc while pushing the volume a bit on the extreme side.
Once again, Replaced the 5U4 to an NOS Sylvania, No arc after 20 minutes of hard playing. But I am guessing its borderline and its best to just fix the problem. a .90cent cap? or a 18.00 tube? I'll replace the cap.
The 2-5U4's tubes that arced had very low miles on them and came right out of a couple working units. ( Known good tubes)
As far as noise goes. Its not an issue. These are very quite amps, or at least mine are. The only real noise I get is from the poorly shielded guitar I am using for testing.
Trout
maxwedge said:Cool
I just finished (almost) a black face Twin with the 6G8 twin tone circut. I use a Weber WZ68 copper cap rectifier. It's like 2 GZ34 tubes. If you go solid state you won't have to worry about too much capacitance.
I've got a thread about my amp over here
Thats a great looking job you did there!! Good Thread also.
I changed out the cap, no arcs "YET"
Interestingly though, When I compare the My Super 5D4 PS to the 5E7 I am a bit puzzled. I have been running 3X30UF on my supers and it never arcs the tube. I am a bit puzzled about why this one does.
I have the 6L6Gc's biased dead on -40V now and it seems really sweet. I plan on {hopefully} going to KT77's yet today.
I may just pop for the copper cap or someones plug in SS replacement. Nothing wrong with more POWER!! lol.
This was my first eyelet board amp. Generally I go real old school point to point, Here is the underside of one of my 5D4/537 Hybred
I'll get a picture later of the one I finished today.
BTW,It will be turrets on the next unit, My eyelets though easy to work with were a bit small and anything over 3 leads was a very tuff fit.
Trout
I Think I found It,
When I swapped out the 6L6's I heard a rattle inside. On closer inspection, There appears to be a piece of metal floating around inside. I may have had a intermittent short in that tube.
I have the new JJ KT77's in it now, I am not exactly sure what my bias voltage should be so its set at -40. Seems ok so far, My ears are to fried to go another 30 minutes at this volume so Its break time until tomorrow.
Clearly the fixed bias version has considerably more verb that the cathode biased circuit.
The OPT is sweet, much better dynamics than the ones I had previously purchased.
This one looks similar to the bassman transformer everyone seems to be selling, But it has 2,4,& 8 ohm output taps. Its about 3 lbs heavier than a normal bandmaster transformer.
Tubes and More stocks them, I got mine elsewhere though.
Transformer Link
Now I need to build a nice Tweed 4X12 cab with some greenbacks
Trout
When I swapped out the 6L6's I heard a rattle inside. On closer inspection, There appears to be a piece of metal floating around inside. I may have had a intermittent short in that tube.
I have the new JJ KT77's in it now, I am not exactly sure what my bias voltage should be so its set at -40. Seems ok so far, My ears are to fried to go another 30 minutes at this volume so Its break time until tomorrow.
Clearly the fixed bias version has considerably more verb that the cathode biased circuit.
The OPT is sweet, much better dynamics than the ones I had previously purchased.
This one looks similar to the bassman transformer everyone seems to be selling, But it has 2,4,& 8 ohm output taps. Its about 3 lbs heavier than a normal bandmaster transformer.
Tubes and More stocks them, I got mine elsewhere though.
Transformer Link
Now I need to build a nice Tweed 4X12 cab with some greenbacks
Trout
Can you discribe the difference in sound from the KT77 and 6L6's?
I've read you don't have to rewire the sockets to go from 6L6 to KT77.
PS: I have the new (reissue Russian) Tung Sol 5881's in my amp and they sound great. The plate voltages need to be kept under 450v with these.
Also you should be measuring your current that flows through the pwr tubes instead of looking at neg voltage. Use a 1 ohm 2 watt resistor to ground in the cathode circut. Read accross it in mil volts....this equals mil amps because of ohms law.
Anyway a bunch more info here.
I've read you don't have to rewire the sockets to go from 6L6 to KT77.
PS: I have the new (reissue Russian) Tung Sol 5881's in my amp and they sound great. The plate voltages need to be kept under 450v with these.
Also you should be measuring your current that flows through the pwr tubes instead of looking at neg voltage. Use a 1 ohm 2 watt resistor to ground in the cathode circut. Read accross it in mil volts....this equals mil amps because of ohms law.
Anyway a bunch more info here.
Hmmmm ,
I am not great at subjective descriptions but I will give it a whirl.
According to The Eurotube (reviews section)website they need to run no less than 20+ hrs before you hear the best improvement.
A lot of guitar guys have reviews there on these.
With 30 minutes or so on a Matched Pair they do sound different than seasoned 6L6GC's. Most noticeable is the bass tightness. Mids seem to have a great deal of bark (supposedly with break in this should smooth out) Highs are very crisp. But not exactly in an EL34 harshness kind of way. I detect a bit of 6V6 type sparkle which I hope stays.
I need to experiment on the bias voltage a bit and see if there is a sweet spot. Right now I set her at -40V (May be to much)and they seem plenty happy, No hint of overheating, In fact, I am fairly impressed at the fact that they seem cooler than the 6L6's.
Actually, ( I learned this from the great guys on this forum)
They may indeed need a minor mod. And depending on the amps socket wiring possibly more.
You have to tie pin 1 to either ground or pin 8. Some amp makers used to use the Known not connected pins for mounting the grid resistor which may need to be moved. It varies from amp to amp. Its nice having the grid resistor mounted on the socket, But 1 side on some amps will need lifted.
On my setup I tied pins 8 &1 together because they both needed to be grounded. Pin 5 & 6 to mount the grid resistor
Other than that, Drop in works great. When I built this amp I planned on these tubes so I wired it accordingly.
I need to document all the key voltages sometime today. My gal is making me a nice chart
I figure maybe 10 more hours before I change anything then I will decide what it needs, Gotta let that newness wear off
Trout
I am not great at subjective descriptions but I will give it a whirl.
According to The Eurotube (reviews section)website they need to run no less than 20+ hrs before you hear the best improvement.
A lot of guitar guys have reviews there on these.
With 30 minutes or so on a Matched Pair they do sound different than seasoned 6L6GC's. Most noticeable is the bass tightness. Mids seem to have a great deal of bark (supposedly with break in this should smooth out) Highs are very crisp. But not exactly in an EL34 harshness kind of way. I detect a bit of 6V6 type sparkle which I hope stays.
I need to experiment on the bias voltage a bit and see if there is a sweet spot. Right now I set her at -40V (May be to much)and they seem plenty happy, No hint of overheating, In fact, I am fairly impressed at the fact that they seem cooler than the 6L6's.
Actually, ( I learned this from the great guys on this forum)
They may indeed need a minor mod. And depending on the amps socket wiring possibly more.
You have to tie pin 1 to either ground or pin 8. Some amp makers used to use the Known not connected pins for mounting the grid resistor which may need to be moved. It varies from amp to amp. Its nice having the grid resistor mounted on the socket, But 1 side on some amps will need lifted.
On my setup I tied pins 8 &1 together because they both needed to be grounded. Pin 5 & 6 to mount the grid resistor
Other than that, Drop in works great. When I built this amp I planned on these tubes so I wired it accordingly.
I need to document all the key voltages sometime today. My gal is making me a nice chart
I figure maybe 10 more hours before I change anything then I will decide what it needs, Gotta let that newness wear off
Trout
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