Seeking for el84 amp schematics with concertina PI

[kagliostro]

I'm looking for schematics of amps with concertina PI and el84 as power tubes

Many Thanks

Franco

[pdf64]

https://el34world.com/charts/Schematics/files/Gibson/Gibson_ea_35_devon.pdf

https://el34world.com/charts/Schematics/files/Peavey/Peavey_classic20.pdf

https://el34world.com/charts/Schematics/files/Vox/Vox_nt15.pdf

[66Strat]

The EA35 schematic looks like a winner.

[kagliostro]

Many Thanks pdf64

66Strat unfortunately I was looking for a 3 triodes preamp and the EA35 is the only among 3 that has a pre with only 2 triodes

all starts from the request of a forumer at DIYItalia, he has a Geloso 1022 and want to convert it to a guitar amp



and it uses 3 triodes as pre the fourth is a concertina PI

Franco

[danhei]

@kagliostro have you/he tried running a guitar into the Micro and Fono inputs? It might already sound pretty good as it seems pretty close to a guitar amp already. And the design looks good. At a guess Micro will have too much gain but Fono could sound pretty sweet.


If you start modding I’d recommend to mostly leave V2 and the power amp alone. Maybe change the first stage from grid leak bias to a conventional cathode bias stage. If it’s too bassy reduce the coupling caps. Harsh distortion try disconnecting the NFB or increasing the value of the 47K NFB resistor.

[kagliostro]

Ciao danhei

I've one but at this time isn't mine that is planned to be restored and modded for guitar use

Micro inputs 4mV (0.5MOhm) (-82.8dB)
Micro gain +118dB

Fono inputs 130mV (1MOhm) (-54.2dB)
Fono gain + 89.4dB

Bandwidth 30Hz - 15000Hz

Power 20-30W



The choice of the guy at DIYItalia fell on a Merlin's Mid Gain preamplifier so will be used V1 and 1/2 V2, the other 1/2 of V2 is and continues to be the Concertina PI



Years ago one other guy modded a 1020 A, he stopped to the first triode with something like this



and he told the sound of the amp resulted no longer as boxy and gloomy as before and was happy with that, so you are not wrong at all

Franco

[Cliff Rogers]

Have a look at the 18Watt Lamington.
https://valveheaven.com/diy-amp-designs/diy-amp/design/

[tubenit]

I have not built this one but it's an idea I drew up a few yrs ago.  I do currently play a 6BM8 amp that's similar using a mosfet CF and 5879 in V1


With respect, Tubenit

[kagliostro]

Thanks Cliff Rogers & Tubenit

I like the James Tone Control in the Lamington and also the pentode as V1 with the Source Follower in V2 of the HoSo56

Both are interesting circuits

I'll submit it to the interested guy

@ Tubenit

I've find a layout for an HoSo56 with FX, there is one specific for the version of HoSo56 you posted here ?

The Geloso G1/1020 A has a very compact Eyelet Board (two rows) the measure of the Board are 3.7cm x 16.5cm and there are 21 eyelets on two rows


it has a montage on the chassis a la Hoffman Stout, sockets and pot are on the same side


 
Franco

[tubenit]

I've find a layout for an HoSo56 with FX, there is one specific for the version of HoSo56 you posted here ?

Yes, but it's for 6V6's, so just change the power tube and cathode resistor out in the drawing.

If you don't have access to 5879 pentodes then you could use a 6AU6 or a 5654 instead.

With respect, Tubenit

[sluckey]

Here's another circuit to add to your collection. It's the AO-43 reverb amp from a Hammond organ.

[kagliostro]

Many Thanks Tubenit

That is really a very good documentation

Many Thanks also to you Steve

Only that it sounds a bit sibylline to me, to modify a Geloso PA amplifier for guitar use, you share the schematic of an organ amplifier that is normally used as a basis for conversions into a guitar amplifier 

However Many Thanks 

Franco