5e3 loosely and heavily modded (first build)

reddiablos

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hi
building a amp around the 5e3 , please note ... it could all be subject to change
here are some pics , its just in concept phase , schematic to follow ... still early days

my mods; hopefully

1 input and bright switch
parallel triode preamp(12ay7) with led biasing and tank circuit between grids
tmb tonestack
fixed bias
send/recieve ports

please note this a test rig build

feel free to comment

regards red
 

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reddiablos

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unfinished schematic but got tank circuit in it. which is just a cap(bipolar) and inductor in parallel which can be tuned too choosen resonance freq by various values of L and C... Fr=1/(2 x Pi x sqrt(LC). the trick is too get a large inductor which comes with higher dc resistance(coz its larger) and should/maybe/hopefully give a bit resonance between grids creating more intermodulation in both valves. or it could do sweet nothing...
wont know till i build it.... hears hoping
 

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andrewRneumann

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unfinished schematic but got tank circuit in it. which is just a cap(bipolar) and inductor in parallel which can be tuned too choosen resonance freq by various values of L and C... Fr=1/(2 x Pi x sqrt(LC). the trick is too get a large inductor which comes with higher dc resistance(coz its larger) and should/maybe/hopefully give a bit resonance between grids creating more intermodulation in both valves. or it could do sweet nothing...
wont know till i build it.... hears hoping

I admire the spirit of experimentation, so don't take this as a knock against the idea. Have you modeled the expected response? One thing I notice right away is that no signal *current* can pass through the tank circuit (except what Miller capacitance and grid leakage will allow). I think that's going to limit the effect--whatever the effect will be. You will also have to consider phase in this arrangement. The phase at the resonant frequency changes drastically--and you are recombining it with the in phase signal from the other valve. Maybe you have looked at all this... let us know if anything interesting happens!
 

reddiablos

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hi andrewrneumann
the phase change of signal is what i'm after and i thought the coil/cap circuit will hold a charge so G1=input sig + tank sig and G2 = tank sig. So now ive got to model 12ay7 freq responses, it might just be easier to build and scope g1 g2 with sig gen lol. will let know how i get on with modelling and build
 

2L man

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Tone stack and volume are strange when they connect to HV? HV thtu vol pot definitely ruin V2a bias!
I am skeptical that LC circuit does anything on other triode control grid?
Also common anode resistor might restrict triodes operation individually. Perhaps it is better to use individual anode resistors and mix trioder output using series resistors? Or install LC circuit to other triode output?
 

reddiablos

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tx 2l man, i am coming to the same conclusion on the LC circuit but got the parts , so why not build it . i can always remove and short g1/g2 on v1ab. seperating anode RL and having LC off anode then mixing resistor is a great idea but calls for more expensive parts but like leo fender I'm cheap. As for the first point about HV thru vol pot on v2 we are talking about approx 5v max coz its gone thru tonestack caps. similar to princeton amps circuit.
regards red
 

loopfinding

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Are you looking for less dirt? Paralleling the input triode won’t really match the gain capability of a recovery stage. You’ll end up with the dirt more akin to a non-reverb BF Princeton rather than a PR. Aside from whatever cathode experiments you’re messing around with, if you’re doing fixed bias, TMB, and dropping a recovery stage, you might want to look at an AA964 schem as a basis instead.

In mine I paralleled the input (though with 6G3 biasing values) but I opted for a single tone control and a coupling cap blend before it (a cathode bypass cap blend works too, I might change to that) for minimal insertion loss. At some settings you still get somewhat of a scoop, which with NFB is good enough for my purposes. The “bug” of gain loss of the bass control works well as a bonus feature for the hotter output of humbuckers. Also makes the end of the volume travel more fine/detailed before you get to splat land.
 
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andrewRneumann

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tx 2l man, i am coming to the same conclusion on the LC circuit but got the parts , so why not build it . i can always remove and short g1/g2 on v1ab. seperating anode RL and having LC off anode then mixing resistor is a great idea but calls for more expensive parts but like leo fender I'm cheap. As for the first point about HV thru vol pot on v2 we are talking about approx 5v max coz its gone thru tonestack caps. similar to princeton amps circuit.
regards red

I think @2Lman is talking about the fact that where most tone stacks and volume controls shunt signal to ground, you are shunting signal to HV. That seems pointless (sorry) and dangerous (HV on control pots). Was that just a drafting error?

Your bias LED is backwards too.
 

reddiablos

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absolute face palm , yes , you are correct tonestack should be going to earth not the HT side (it was there and i just couldnt see it) and diode wrong way . thanks guys ... all i can say is rather now than later

@mountainhick you are spot on
@2L man Sorry my bad
@andrewRneumann absolutely drafting error

i am now gonna do the walk of shame, then edit with crayon the schematic

 

mountainhick

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absolute face palm , yes , you are correct tonestack should be going to earth not the HT side (it was there and i just couldnt see it) and diode wrong way . thanks guys ... all i can say is rather now than later

@mountainhick you are spot on
@2L man Sorry my bad
@andrewRneumann absolutely drafting error

i am now gonna do the walk of shame, then edit with crayon the schematic


No Shame, easy to do. It's great to have extra eagle eyes and review from this forum! I also have drawn diodes and caps in wrong polarity, dead shorts, missed connections etc.
 

reddiablos

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just a heads up, there will be more revisions.

things to do

fixed bias circuit
PI balancing pot (maybe move non inverted output to below 1k)
grid bias balancing pot for 6v6's(coz ive got old mismatched tubes)
recheck values of LNFB on v2a
maybe add presence v2b
send and receive

Do i want it all? yes .

@andrewRneumann As for +250Vdc on grid , only if its biased correctly.
 

reddiablos

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small update.... modelled 12ay7 in ltspice or rather someone else did, and i took nearly two days to workout one simple command line ".inc", tx andy nearly went grey. here's a pic of the inductor/cap freq response on outputs(not a massive effect). yet too model led's, but decided on common RL(mix in tube)

reasons for led

merlin likes em and they have been used before, plus these modern built leds are being well made low noise(may remove 100nf noise cap on schem) , constantish response to current , no need of bypass cap

reason for dual triode

higher current (keep led fed(5ma)), more power feed tonestack,lower Z always good for driving.

anyway wishing you all well, regards red.

ps thoughts and warts welcome
 

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reddiablos

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@loopfinding
your post was "great" , it got me thinking( the diode bias is gone (wont fit)) and a complete change of tonestack to more match the original, while it was also the "worst" for the exact same reason LOL

find attached
 

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reddiablos

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ok latest design specs

whats your views on lower loads(gain) on v2 amp + PI (33k +66k) with respect to tone , i know a subjective question(personal taste).

damn,while writing just had an idea for tank circuit addition...

ok, ill post schem and current preamp up for review and critique
 

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reddiablos

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answer my own question, the crazy idea of where to put LC circuit on a "trioder" k1-g2 on v1ab....of too research
 




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