Stuff you wanted to know but were afraid to ask

Good you got it sorted! I hope you found that you picked up some methodology etc along the way, that will help further on down the path towards pedal build obsession.
A bit surprised that the order is different from the doc.
"Mode is a rotary switch that selects between four different tone modes: Off (tone bypass), 1(scooped mids), 2 (flat mids), and “Cheese” mode which biases the transistor into instability."
On the other hand if you are labelling according to the original then "1" and "2" does not say much about the audio aspects anyway.
 
I’m not fluent with SPICE and didn’t solve this earlier today, so could someone give some insight what’s going on this circled section?

IMG_8571.jpeg

Treble bleed between 100+150K, lower freqs see 250K, but 50nf via 5.1K to gnd. 150K+50nF create lowpass, but how 5.1K affects here?
 
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JohnnyCreepy said:
One ch for stringed instruments and two for mics, keyboards etc.
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back when PA systems were still tube you wanted to drop bass off the channels that weren't mostly highs (like mics) partly from amp design, partly from the speakers expected to be hooked up to them ... along with some signal loss since we're eventually mixing these various inputs and don't want to wildly compensate for one being hotter than another
 
ICTRock said:
back when PA systems were still tube you wanted to drop bass off the channels that weren't mostly highs (like mics) partly from amp design, partly from the speakers expected to be hooked up to them ... along with some signal loss since we're eventually mixing these various inputs and don't want to wildly compensate for one being hotter than another
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Well that might explain why the latter 2xEL34 PP output stage isn’t loud enough when using instrument/bass channel vol pots dimed. With enough drive from dirt pedals I need to turn back amps vol pots.

So far coupling or bypass cap changes hasn’t helped with the lack of ”clean” output power. Also no luck on adjusting preamp and corcertina stages bias point. One by one been replacing original Rifa coupling caps

Now it’s a great amp for night time garage jams without annoying neighbours too much, but don’t you agree that with B+ idling at 440Vdc and good iron surrounding 3x12ax7 & PP El34s SHOULD be inducing tinnitus even without pushing the front end with pedals!
 
PA and organ amp conversions are always tricky and I don't miss doing them.

not to be that guy but the schematic snippet you shared shows 12ax7 tubes using contact bias which is not what you want in an instrument amplifier. try RCA tube manual values like 100K plate and 1k5 cathodes (bypass cap to your taste) instead of the 220K plates and no cathode resistors shown.
 
ICTRock said:
PA and organ amp conversions are always tricky and I don't miss doing them.

not to be that guy but the schematic snippet you shared shows 12ax7 tubes using contact bias which is not what you want in an instrument amplifier. try RCA tube manual values like 100K plate and 1k5 cathodes (bypass cap to your taste) instead of the 220K plates and no cathode resistors shown.
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I’ve done some tweaking already. Instrument CH gain stages are 220K/2.4K, V2 220K/2.2K+bypass cap and 220K/1.5K+bypass cap. PI is concertina 62K/1.5K+62K.

From my understanding this one was mainly marketed as a bass amp. It’s Dynacord Bass-King. I can relate modding is hard with this too as chassis on accepts power tubes horizontal and PCB is holding circuit on an open frame. This leaves one triode pair unused! Main purpose buying this amp was salvaging trafos and tubes so maybe I’ll ditch the OG chassis and circuit completely here.
 
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