old tape recorder to vox ac4

[Kesi from Hungary]

While I was working at my Hungarian neighbor's house this summer, I came across an old tape recorder in the attic.
It immediately caught my interest because it turned out to be a tube device.

It is a Hungarian Vörös Szikra magnetophone (translation: red spark) from 1954.
It has 2 channels. There is a radio section that was tuned to 1 fixed channel. Another part is the tape recorder part that could also record via the radio or a microphone.
Full wave rectifier AZ4, one EM4 and for each section an eec40 and a el41.

A few weeks went by and I asked my neighbor if I could take over the magnetophone and that was okay. I was very happy with that and I had a nice project for the winter months.

Because the el41 is a predecessor of the el84, perhaps interesting enough to make it a vox ac4. In the old schematic I see that the power transformer provides 280V. Should that be a good match?

I understand that it is recommended to stick to the original power section as much as possible during a conversion. Could I continue to use the AZ4 or should I switch to the ez80 from the original vox ac4 scheme.
 
I also have a nice 6p14p ev, 6N2P tube and a 6j32p in mind.

Franco was so kind to share  some schematics and layouts.

What do you think?
Can this become an ac4?

[PRR]

> Can this become an ac4?

Why? The world is full of those. Who else has a Vörös Szikra Red Spark guitar amp?? Unique in the whole world, I bet. I used to work with a bunch of ex-Hungarians (got out in 1956?), radio/TV engineers, and they'd be upset you cut-up a Vörös Szikra.

And the schematic is a LOT like most SE guitar amps. Go in at Micro and bypass the source/tape and speaker select switches to always-on. Yes it is the two-triode preamp family instead of the pentode-preamp family....  there's enough sockets and switches to add just the preamp of a AC4.

The only thing crying for a change is the bias network common to two triode stages-- when that cap gets old it will motoboat. Today R and C are cheap. Use two 2.2k and a selection of 10uFd and 6.8uFd.

[PRR]

Vörös Szikra was also making special-purpose transmitters in that era. Or so the US CIA thought. Partly declassified in 2008 but note some items were still redacted.

Eight-ten 100KW transmitters a month is a lot. US AM broadcasters bought rigs like that but nowhere near that quantity. If true (not a CIA fantasy) then Vörös Szikra must have been one of the largest transmitter factories in the world.

[Kesi from Hungary]

> Can this become an ac4?

Why? The world is full of those. Who else has a Vörös Szikra Red Spark guitar amp?? Unique in the whole world, I bet. I used to work with a bunch of ex-Hungarians (got out in 1956?), radio/TV engineers, and they'd be upset you cut-up a Vörös Szikra.

I understand what you're saying, PRR. I was also unsure whether or not to do it.
The tape part does not work and parts are missing.
The neighbor's husband was a village electrician and has worked in the area on a lot of radios, televisions and has tinkered with a lot of equipment here. The attic used to be full of boxes of tubes and other things. This was about 40 years ago. And the tape recorder has also undergone quite a bit of tinkering. I don't think I can restore or use the old setup.

But I can report that the Vörös Szikra magnó is cherished by radio amateurs and collectors and that it is occasionally offered on the internet or at a fair.
There are still videos circulating on YouTube

[kagliostro]

Not sure about but I think PRR say you can dismant the parts not necessary, maintain and ripristin to use the part inerent the audio amp and adapt a guitar input on it

Franco

[Kesi from Hungary]

Okay. I understand Franco.
Thank you for explaining. I just wanted to point out that the tape recorder is now a mess. The outside too, actually 

[Williamblake]

Take what you can. Give nothing back! Think of it as reincarnation.