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Joel 30th October 2002 03:06 PM

Hammond 850Q Interstage?
Does anyone have any experience with this 1:4 interstage? Their site gives its specs as +/- 0.5 db max. from 20 Hz. to 20 Khz - seems the best I've found (for the money).

I was considering 01A --> 850Q --> 01A --> 71-A or 45, single ended of course.
Damn 01-A's can't swing the 80V by themselves.


Colt45 30th October 2002 09:18 PM

I'd save the 01A's for the radio fanatics, and find something with a little more gain, myself.

I got some old 01C's if you need them ;)
(same as 01A, but 1/16amp filament instead of 1/4amp, IIRC).

dice45 31st October 2002 12:18 AM


20kHz upper BW limit is not enough.
1:4 IS trannies tend to limit BW. I would go for 1:2 or 1:1 IS trannie.

A 71A can be driven by a 56 or 76 with choke or CCS or 1:1 IS primary as load.
With a 45, it becomes a bit tough, then 1:1.5 IS might be preferable.

Joel 31st October 2002 01:26 PM


I AM one the radio fanatics! Regularly pick up Radio Havana from Cuba with a single 01-A as a regenerative receiver. That's 1,200 miles. Not bad for 1925 technology.


fdegrove 31st October 2002 01:30 PM

Hi Joel,

I noticed a few of the tube guys here are collectors of old radios too.
I think Tom Bavis is being one of them but there must be others.

Any chance of picking up a couple of Partagas cigars while you're at it?:D


Joel 31st October 2002 01:47 PM

Sorry Frank, but Cuba is off limits to us Americans...

Colt45 31st October 2002 06:44 PM


Originally posted by Joel

I AM one the radio fanatics! Regularly pick up Radio Havana from Cuba with a single 01-A as a regenerative receiver. That's 1,200 miles. Not bad for 1925 technology.

Cool, ive been thinking of doing that as well.

I'd need an interstage tranny and a 4pin socket though, which I am lacking at the moment.


Joel 31st October 2002 06:49 PM

no iron necessary
2 Attachment(s)
I know it's a bit off-topic, but here's the schematic I drew up for that receiver I've been using. There's no step up transformer needed (since the detector is the audio amp as well. You will need a set of high impedance headphones though (1,000 to 2,000 ohms). All of the parts are very cheap. Angela Instruments, or Antique Electronic Supply have 4-pin sockets.

Colt45 31st October 2002 07:45 PM

ok, cool.

I was going to replace the headphones with an interstage, and feed it into a 6V6 or some other pentode.. maybe something that likes a nice low B+. (maybe a gain stage between the two tubes, i suppose..)
so I can drive a speaker with it.

whats the specs of the two coils marked T and S ?

I'd order a socket from somewhere, but by the time it gets here, and i pay for it, and shipping.. well its just not worth it for a measly socket.

I suppose you could probably make an ok regen reciever with a 6SN7 or 12AU7, etc etc,. first half for detector/amplifier, second as a gain stage to drive an amp..
(i might as well use one of my 01c's, they're not doing much good sitting here.)

Joel 31st October 2002 07:54 PM


You need the headphones. Distant stations are tough to hear, and listening on a big speaker would be fruitless, even with the extra amplification. has them for $17

"S" and "T" are coils wound on the same form, 1/8" apart from each other. I use a 4 pin tube base from a burned out 01A. Any base would be fine. I have "S" as 16 turns of #24 enameled wire, "T" is 9 turns. This seems to bring in stations in the 5-8MHz range. Make sure both are wound in the same direction.

So, actually you need two 4-pin sockets, a tube base, probably a rheostat and the variable capacitor? Now it may be worth an order, huh?

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