Geloso G213A

[Sk10]

Hey Guys,
I I saw a Geloso G213a for sale locally for a low price.
Is this a good project to convert it into a guitaramp?
Thx!

[loudthud]

Looks good for a conversion. It has fixed bias for the outut stage and DC heater supply for the preamp.

[Sk10]

thx, that's what I was thinking....
Is a conversion to a 5E3 circuit realistic?
.

[loudthud]

The problem with the 5E3 is the 9 pin preamp tubes. You would have to fabricate a cover for the Octal socket holes to install the 9 pin sockets. Weber sells such an adapter, but they are frequently out of stock. I would stick with the Octal preamp tubes. There are earlier versions of the 5E3 that used octal preamp tubes. I think the 5C3 is one. Lots of possibilities with two dual triodes and a pair of 6V6s.

There is no currently make 12SL7, but you can get the 6SL7 which is just a 6V version of the same tube. You should be able to find New Old Stock on the 12SL7 and they should be fairly inexpensive because demand is low.

[Sk10]

5c3 might be interesting, but I see 2 problems:
1 As I search the web there seems to be a general consensus that a 5c3 circuit doesn't work that well with pedals.
2 How do I organise the heater supply. In the original schematic of the donor amp the heaters of the preamp tubes are in series (Total 24V) Can I reuse this part of the circuit with two 6SL7's?
The common noval tubes (12AX7, 12AY7) have center tap on their heater, so they can run on 12V

Conversion plates octal 2 noval aren't a problem. A local store has them.

thx for your reply!

[Sk10]

I finally bought the Geloso last week
Also got some ancient DIY amp, but it has good glass and transfos. (2x 6SL7 2x6V6, all RCA)

[Sk10]

Two weeks ago, I finally did the conversion. I'm very pleased with the result, it sounds very nasty.

The inputs are lo & hi sensitivity. The switch below the inputs selects the channels: instrument, mic & linked.
On the back, I added a 230V IEC Power inlet. I also removed the output terminal strip and replaced it with an ordinary output jack and a 4-8-16ohm switch.

I used the stock 5e3 schematic, so I replaced the octal preamp sockets with noval ones.

Th only problem I currently have, is the instability of the DC preamp heater supply. I temporarily need to use a 24V voltage regulator until I redesign this part of the heater supply .