Modify a EL504 Bassman Clone to 6L6 ? ( Sound Thunder 90)

[wahmi]

Hi all.

So far I have only made amps kits and would go to the next level.

I use and love an old copy of Bassman 50 made in Italy that delivers 45W and out in 12 ohm. It's one of my favorite amps but it's not very user friendly.( like all bassmans..)

It's a Sound Thunder 90. The power section is built around 2 EL504, which are TV line scan tubes. I would like to swap theim to 6L6 or EL 34 (but preferably 6L6) while adding:
- a triode pentode switch, to switch to 20 watts or even less.
-An effects loop
-a master volume

I saw that the modification already exists on the silverface bassman.
https://www.tdpri.com/threads/5f6a-bass ... E46bHT9MT4


I don't care about the cost of modifications because this amp has sentimental value.

I am trying to raise the circuit, but for the moment it looks a lot like the FBT BASSORGAN (except for the power section which is in EL503.)

on picture the power section of my Sound.

The preamp section is separated into another chassis and built on a PCB.
I started a draft layout ( to be continued for power section).

What do you think about 6L6 swap,do you think sound will be really better ?(EL 504 are very cheap and strong).
What do you think of the technical feasibility of this project? do you have any advice for picking up the diagram? One of you al

[roberto]

Like most tv tubes, EL504 need a low screen voltage compared to the plate voltage ( https://frank.pocnet.net/sheets/010/p/PL504.pdf ).
A 6L6 with that screen voltage wouldn't perform as it should. Also, it has to be checked the OT to see its impedance and current capability.
Most probably a conversion to 6V6 with some mods would be easier and would fit better.

[wahmi]

i was thinking to swap with this transformer.

https://www.tubeampdoctor.com/en/output ... an-ten?c=0

[roberto]

Isn't easier and cheaper to sell it as is and build another one as you like?

[pdf64]

The idea seems ill advised to me
Why not use the amp to its current strengths, eg as a clean pedal platform, a wet only satellite rig, acoustic / keys / bass amp etc?

Won’t gutting it and completely changing its character detract from its sentimental value?

Cheap, strong, easily available NOS valves seems a massive benefit to me.

[wahmi]

your opinions are very interesting.

2 reasons why I would like to change:

-he need to be completely revised (tubes, filtering, and certainly other things). I got Humm,buzz, volume down etc...

-I'm afraid I won't be able to find EL 504 NOS for very long.

To tell the truth, it already sounds great with guitar and it can crunch in organ channel at high volume

think possible to let it "stock" and install a 45/20 w switch (or less) and a loop?

[Stevem]

You very well might find that running that output stage in Triode will not sound that great at all!

[Phil_S]

If you don't care about cost, then order a kit and build it. It will be simpler, probably less expensive, and more likely to be a success. Where are you located? Maybe someone will suggest a place to order a kit.

[roberto]

I'd really invest in building a new amp, and sell this one as it is.
EL504 will be available for a long time, and you can still buy 10 of them and consider them a legacy for future generations of guitar players.

[wahmi]

So thx all.

I will made all the schematic for me and "history"

Do you think it can be a good idea to build other project with EL 504 ( for very low cost projects).

Think i will try to make me a 20 watts Bassman.

[ChopSauce]

Why bother running out of EL504 tubes?

If you like the amp as much as you write, just do the minimum number of mods to make it more usable / improve it (the easy way) "à la petite", as say the southerns
(the french ones... )

You very well might find that running that output stage in Triode will not sound that great at all!

Likely, yes.

NB gutting an amp to rebuild another one with its parts is a more valuable idea if you can reuse its transformers - if that is something of what you have in mind -

[wahmi]

It was an opportunity to continue learning about a worthless amp.

I think about a master volume and a loop ( deactivatable). ( à la petite comme disent les gens du sud )

The preamp is physically separate from the power stage, the loop location should be easy to find right ?

[wahmi]

here the preamp ( Bass only).

I think i can try some simple mods.

What do you think about this section ?

[ChopSauce]

here the preamp ( Bass only).

I think i can try some simple mods...

That looks pretty straightforward, yes.

[wahmi]

i began a layout of power amp.