Ideas for 4v filament triodes/pentodes

[Hendrixon]

Hi,

I found an oldddddd (1937/8) german tube radio - Mende 315w - in a flea market that looks like it would make a nice SE guitar amp.
Tubes inside are:

AL4: Output Pentode
AZ1: Rectifier
AC2: Triode (gain stage before the AL4)
ACH1: Triode/Hexode
AF3: H.F. Pentode (variable mu?)
AB2: Dual diodes
AM2: nice fish eye

Filament winding is 4v, so I'm looking for recommendations on suitable tubes, mainly triodes for preamp use (high mu will be cool of course) and even other pentodes.


Thanks

[ray_moth]

I used to buy old radios from jumble sales when I was a kid in England. Some of them had 4v tubes but none of them was any good! Mostly B7A and B9A bases, all indirectly heated. I wouldn't recommend the 4v tubes for any pupose I can think of. Also, it's hard to find any useful data on them, or even to find tube sockets that are fit for use.

[AndreasS]

Originally posted by Hendrixon
...
AL4: Output Pentode
AZ1: Rectifier
AC2: Triode (gain stage before the AL4)
...

A good single ended amplifier...

Regards
Andreas

[Merlinb]

+1 on what AndreasS said- use the recitfier, power pentode and preamp triode.
You can always add a small 6V or 12V transformer to power some other "common" valve types.

[Hendrixon]

Yup that is pretty much what I thought to start with (AZ1/AL4/AC2), but from bits of info I've learned that the AC2 (the single triode) has a gain factor of only 30, which I doubt will be enough to amplify a guitar enough to drive the pentode...

Maybe back then things worked differently? who knows
I'm thinking maybe to add another AC2 if there aren't any other options for 4v triodes. with a boost pedal this should probably give a nice woody blues sound

At the concept level I prefer not to use more modern 6.3v/12.6v tubes (and other parts in general) here as I want to keep the *vibe* and sound of what this radio used to have 70 years ago, when the engineer that desinged it, the assembly tech that built it and the first customer who bought it, enjoyed

[kevinkr]

Use modern tubes for a guitar amplifier, AZ1 and AC2 are expensive, as are the sockets required to use them. The radio itself if intact may have significant collector value and might better be sold on eBay to finance your venture.

What you probably want is a couple of 12AX7A/ECC83 and a 6BQ5/EL84.

Most radios built in that era would hardly be suitable for such use, and weren't designed to produce the kind of distortions you are seeking. I've seen output transformers and speakers not intended for MI use smoke pretty quickly when abused..

[ulibub]

Hi Hendrixon!

Be careful with microphony on these old tubes - many of them are incredibly microphonic. You also can use the AF3 as an AF amplifier (it is a remote cutoff (variable-mu) pentode, that time still not with gliding screen voltage), its nonlinear characteristic perhaps might add some nice "tube sound" to your guitar amp. And you could do alike with the ACH1 (triode-hexode, triode grid internally coupled with the second control grid of the hexode)

But I fear that you might be limited using them especially in a guitar amp with high amplification..... the input stage might be very critical due to micrphony. I once built such an amp (with AK2 - AF3 - AL4) just to see how it works, and it even got into self-oscillation by microphony when it was too close to the speaker.... And this was not a guitar amp.... Maybe an input stepup transformer would be useful....

Good Luck!

Uli

[unclejed613]

i would go completely "retro" with these, and build a "breadboarded" amp. see if you can get a phenolic or hard rubber plate, about 12"x24", and screw standoffs into it for the tube sockets, etc.... try to get some components that match the era that the tubes are from, and design an amp that looks like it comes from that time period..... wire it with cloth insulated wire. just remember in your design, that those components also predated feedback theory, so little or no feedback was intentionally used in amplifier designs.....