Why then does the Bogen schematic show 450vdc? I understand basic power supply rectification. I thought the caps did some voltage boosting of sorts...
Ahh... didn't refresh. Thanks for the response.
I'm still thinking about it. The 7868's and the 6c4 driver i have are junk, and would need to be replaced. I can put in new sockets and replace the 7868's with the cheaper equivalents, or build from the ground up. I figure if I'm going to do it i might as well build a proven design with new components. If i could save money and use the transformers i have that'd be even better. I'm using a 100db/1w JBL 15" so i really don't need (nor want) more than 4w or so.
What about the output transformer, is that usable? Since I would be using a single output tube do i connect the two existing wires that go to the 7868's together at the 6v6, or just use one lead?
I'm still thinking about it. The 7868's and the 6c4 driver i have are junk, and would need to be replaced. I can put in new sockets and replace the 7868's with the cheaper equivalents, or build from the ground up. I figure if I'm going to do it i might as well build a proven design with new components. If i could save money and use the transformers i have that'd be even better. I'm using a 100db/1w JBL 15" so i really don't need (nor want) more than 4w or so.
What about the output transformer, is that usable? Since I would be using a single output tube do i connect the two existing wires that go to the 7868's together at the 6v6, or just use one lead?
It wouldn't take a whole lot to turn it into a "Deluxe" (see below).
6V6's cathode bias quite well, or you can rework the bias supply for fixed bias if you wish.
for a single output tube, use only one leg and CT of the output transformer. Put heat shrink over end of the other leg to make sure it doesn't come in contact with anything. You would still need to drop the plate supply to around 350 volts. I would use a 10 watt resistor.
6V6's cathode bias quite well, or you can rework the bias supply for fixed bias if you wish.
for a single output tube, use only one leg and CT of the output transformer. Put heat shrink over end of the other leg to make sure it doesn't come in contact with anything. You would still need to drop the plate supply to around 350 volts. I would use a 10 watt resistor.
Attachments
That bogen would convert into a pretty nice PP amp, but the iron would not really work for an SE design.
If it were me, I would save the bogen stuff for something bigger using either 6L6's, 5881's, or possible a 7591A octal.
Not the perfect impedance match on the OT, but they make some really fine sounding Trainwreck style amps.
If it were me, I would save the bogen stuff for something bigger using either 6L6's, 5881's, or possible a 7591A octal.
Not the perfect impedance match on the OT, but they make some really fine sounding Trainwreck style amps.
Trout, I saw that you modded one of the champ circuits to use either a 6lg or a 6v6. I have been wanting to build a SE amp like this but would like to be able to use interchangeably 6v6 6l6 ot KT66..... the early tweed [I'm just finising up a Delux 5c3] were cathode bias as opposed to the later fixed.
I'm a bit new at this but with cathode self/bias is there a way you are aware of to sub power tube at will ???
Good thread
Thanks
Mikecj
I'm a bit new at this but with cathode self/bias is there a way you are aware of to sub power tube at will ???
Good thread
Thanks
Mikecj
Will the bogen iron work okay with the Matchless Spitfire design? If not, what would you suggest? This will be my first real tube project, and because i'm a solidstate fan for hi-fi i'm fairly lost. Thats why i was looking at the champs for simplicity.
I got the bogen for free, along with the JBL 130a so i'd like to see what i can do for little investment.
I got the bogen for free, along with the JBL 130a so i'd like to see what i can do for little investment.
mikecj said:
Actually Yes, there is a very simple way to make it an easy swap with the tubes.
Now Ideally with the Edcor XSE15-8-5K output transformer the primary impedance is 5K to an 8 ohm output. This is a great match up for a 6V6 amp. I have been using it with the 6L6 on a close enough sort of basis.
I put a bias selector switch to correct the bias at pin 8 of the 6L6/6V6. See attached picture.
Now, this is an effective way to make the amp more flexible, but there are a few things to remember.
Use a high quality switch!!
Never change setting while amp is on.
Be certain switch position matches the tube in use.
Due to my anode voltages being a little high, I ended up using corrected values for the cathode resistors. You will possible need to adjust that value on your particular amp/transformer set.
On mine, the 500R is for 6L6GC, the 680R is for 6V6GTA.
The cathode capacitor remained the same for either tube.
I was looking to do 2 things,
#1 not stressing the output tubes to improve life, and #2 using a set of values that will be survivable in the event that the switch is set incorrectly.
On my amp, there is a noticeable volume difference, but the bigger difference was the point at which the amp begins to break up at the volume knob. The 6L6GC breaks up at a higher volume setting and does so less abruptly.
Now, if your into small venues like coffee house or book store type jazz gigs, This amp sounds huge, it has a big full bodied range, no lack of bass, and a nice shimmer/ring to the highs.
It can stess your ears in a bedroom/livingroom enviroment when cranked, but at lower volumes accepts dirt pedals well.
It could be tweaked even further, I just have no need to go further.
Trout
Attachments
Thanks, just the idea I was looking for. I have some good ceramic multi position switches. I'll just have to figure the resistor value for bias for the KT66 and add a third position.
I'll check on the OT you mentioned. Any personal experience with either the Hammond 1600SE series... Or using say a Mercury Magnetics Champ or SE Princeton OT ????
Thanks again. [ I've got 1 [one] NOS Genelx KT66 want to use it in "something" this sounded like a good Idea.
Mikecj
I'll check on the OT you mentioned. Any personal experience with either the Hammond 1600SE series... Or using say a Mercury Magnetics Champ or SE Princeton OT ????
Thanks again. [ I've got 1 [one] NOS Genelx KT66 want to use it in "something" this sounded like a good Idea.
Mikecj
mikecj said:
There are lots of really nice OT's around, Mercury, Heybour Hammond, But try to beat Edcor's price, not an easy task on a good champ sized SE transformer.
I would think the KT66 would run really close to if not the same as the 6L6GC. Best bet is to pop it in, get the voltages and see where it ends up.
I ran an EL34 and KT77 in the amp, but it was not a good matchup, perhaps had I tinkered more with mismatching the speaker to alter the reflected impedance it may have been better.
Stormrider
If it were me, I would be looking at possibly something like a simple PP design using 6L6GC's
One that comes to mind would be the Fender Pro Narrow Panel 5E5 Version .
You can still use the SS rectifier arrangement since the bogen power trans has no 5V tap for a Tube rectifier.
Simple design known for great tone.
If you looking for more Marshall type overdrive, Im not your guy LOL, I have restored a few lead 100's but they were never my cup of tea.
If you can dig up a Sam's Photofacts set on that amp, very often it lists the transformers by brand, You could then look them up in the old catalogs and get the actual transformer specs and often even reccommended replacements.
I have an old Bogen GX50 here I bought the Sams for on ebay for $2.50. I had planned on building it into a Trainwreck with the stock 807 output tubes, But it has been sitting here over a year now, To many projects, to little time.
Trout
Thanks Trout.
Looks like i'll try a Fender Pro then. Some simple questions (wouldn't be any fun with out them 🙂 ).
Can i drop one of the 12ay7 stages? I only need a single input.
Can i add a "master" volume control after the preamp stages so i can have the distortion, but without killing my ears? I play in a small room most of the time. If i understand this right, i would replace the 56k resistor before the 6l6's with a 1M pot, with coupling caps on the legs so no dc gets to the pot, correct? I'm looking at this 5e3 schematic. http://www.ampwares.com/ffg/schem/pro_5e5_schem.gif
I would connect the pot exactly like it is connected in the Spitfire schematic, correct? http://www.diyguitarist.com/Schematics/SpitfireSchematic.bmp
Thanks for the help.
Looks like i'll try a Fender Pro then. Some simple questions (wouldn't be any fun with out them 🙂 ).
Can i drop one of the 12ay7 stages? I only need a single input.
Can i add a "master" volume control after the preamp stages so i can have the distortion, but without killing my ears? I play in a small room most of the time. If i understand this right, i would replace the 56k resistor before the 6l6's with a 1M pot, with coupling caps on the legs so no dc gets to the pot, correct? I'm looking at this 5e3 schematic. http://www.ampwares.com/ffg/schem/pro_5e5_schem.gif
I would connect the pot exactly like it is connected in the Spitfire schematic, correct? http://www.diyguitarist.com/Schematics/SpitfireSchematic.bmp
Thanks for the help.
Stormrider said:
Dropping 1 12AY7 would be pretty simple, I have added a master volume to a very similar circuit and it works great!
In Fact, it had little or no effect on the overal tone quality to my ears.
Take a look at the Master Volume in this drawing.
Simple parts needed, (2) ,022/600V caps, (1) 1meg pot.
I found that you can get some great overdriven tones cranking the pre-amp volume and not get the ear bleeds. It is a different type of distortion though. More of a traditional pedal sound and no output tube growl of a fully cranked amp at low volumes.
I would not use that paulC mod on that page though, it sounds nice, but it appears to be pretty hard on the output tubes.
trout
- Status
- Not open for further replies.