Hey guys,
Just scored on an old Allen Organ amp chassis that I will be using for bass guitar. It uses HUGE power/output transformers, 4x6l6, 2x5u4, 2x6sn7, and a 6au6. I haven't traced out the circuit yet but I'm planning on leaving everything except maybe the 6au6 input tube since my goal is to build in a B15 preamap and run it into the power section. Should be pretty doable, correct? I like the idea of the 4x6l6's as I could pull two of them and run it at half power most of the time.
I cannot find ANY information on this amp/schematic. I've wanted to build a bass amp and knew you needed a large output transformer but this is ridiculous! The pictures below are of one on ebay now, it's identical to mine and shows what I have to work with. I plan on replacing the electrolytics just in case they're on the their way out. I'm pretty damn excited to get going on this thing. I think running it through a couple 15's would be nice...
Just scored on an old Allen Organ amp chassis that I will be using for bass guitar. It uses HUGE power/output transformers, 4x6l6, 2x5u4, 2x6sn7, and a 6au6. I haven't traced out the circuit yet but I'm planning on leaving everything except maybe the 6au6 input tube since my goal is to build in a B15 preamap and run it into the power section. Should be pretty doable, correct? I like the idea of the 4x6l6's as I could pull two of them and run it at half power most of the time.
I cannot find ANY information on this amp/schematic. I've wanted to build a bass amp and knew you needed a large output transformer but this is ridiculous! The pictures below are of one on ebay now, it's identical to mine and shows what I have to work with. I plan on replacing the electrolytics just in case they're on the their way out. I'm pretty damn excited to get going on this thing. I think running it through a couple 15's would be nice...
Moving to the instrument & amps forum per forum policy. You'll get a lot more input for your design questions on I & A.
Congrats on your score! Based on your description, I think you have the guts from an Allen C-3 organ, the amp was rated for 60 Watts. I think it is safe to re-cap it to start with, then you probably want to get rid of the OC3 regulator and run the screen at a higher voltage to get the power up, then adjust the gains of the various stages, and play with the feedback a bit... Looks like a fun project.
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jazbo8: C-3, you nailed it! I've looked for such a schematic but turned up nothing! Thanks for this, it really gives me a starting point to understanding what's going on inside the amp. I've built a couple of guitar amps and repaired some as well but I'm still learning as I go. Think I could remove the first two tubes (6au6 and 6sn7) and slap in a B15 preamp section before the PI 6sn7? I'm really going for the old school soul tone so I think that Ampeg circuit is a decent goal.
This forum is wonderful!
This forum is wonderful!
The B15 preamp is quite different from the C-3, so if you go that route, it is basically a complete gut job, perhaps a mini-SVT? the circuit topology is a bit closer.
Ah, I see. I just figured I could run any preamp into the power section of the c-3. I know it's got two more 6l6's but I'm ok with that 😉 I'm not entirely set on any specific amp. I just want to get a decent preamp section in and get this up and running!
May be I mis-understood you, I thought you want to build the B15 preamp from scratch... if you already have a B15, then it is possible to plug its output into the power section of the C-3 without much trouble.
No you read right, I wasn't clear. I don't have one but i wouldn't mind building a single tube b15 preamp and inserting into the chassis at a logical point before the power section. You're right, it won't really be a b15 but I think any decent preamp/tone stack with this amp would be just fine. I've never seen transformers so big! I think it'll stay in my practice space most of the time...
Yes, with those large transformers, I think you can easily get more than 100W, since the original use was for an organ, the OPT's LF response should be quite good as well.
Just saying, I think you may want to look into saving the 6au6 in the preamp, as not only are they very cheap to get NOS and roll for different tones, but they also have that certain characteristic that only pentode preamps have....
Forget the tone stack, just pop a rack preamp/eq up front or even just a Sans amp and an EQ pedal and see how it does
I guess that is always an option! I do have a sansamp. Now I just need to build/buy a sufficient speaker cab. Was thinking a couple of 12's.
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