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Frankensteining Two Peerless 4722 Input Transformers
Old 25th January 2009
  #1
Lives for gear
 
🎧 15 years
Frankensteining Two Peerless 4722 Input Transformers

I'm a songwriter/recordist trying to come up with possible uses for a pair of Peerless 4722 input transformers. They are octal-based and were originally used by Altec as microphone input transformers in tubed circuits, e.g. the 1567a preamp-mixer.

The most useful item to me would be a microphone preamp. Either clean or colorful would be OK. Stereo transformer in-only or mono transformer in and transformer out would be OK. The recording devices to be fed are all modern-design solid state. Nothing exotic.

...

Ingredients:

Two Peerless 4722 transformers. Lo-Z to Hi-Z (or the reverse, right?).

Bogen DB10A integrated amp - clean, but no longer pristine. A candidate for modification. No longer needed as a power amp.

The Bogen has 5 octal sockets (5Y3GT rectifier, 2x 6V6 outputs, a 6SL7Gt preamp tube, & a 6SF5 preamp tube) and one 9-pin miniature socket (12AT7 preamp tube) - all on the top of the chassis. It has four retro-looking knobs (Volume, Bass, Treble, Input-Selector) on long shafts on the front and a hum-balance control on top. And it has 6 RCA inputs (5 on the non-power supply side and 1 on the back).

...

Optional Ingredients:

Dressen-Barnes model 22-102A regulated power supply (5 tubes) with 150v B+ @ 70 MA and a 6.3v filament tap.

Two Stewart external phantom-power boxes.

Two RCA Tube Manuals.

I'd like to keep the required metalwork on the Bogen chassis to a minimum, but that's not critical.

...

Another option might be to modify a Peavey VMP-2, but the stock piece sounds good to me already. So I'd need to be really convinced to ever mess with that.

Thanks for reading. I'd appreciate any and all comments and circuit/build suggestions. Exotic schemes allowing full use of the Bogen's real estate are also welcome. I've got a few ideas, but only if the thread attracts some attention.

best,

john
Old 25th January 2009
  #2
Lives for gear
 
emrr's Avatar
 
24 Reviews written
🎧 10 years
I'd sell the pair of Altec transformers since they're worth too much. Then replace them with something else. If you want modern, Cinemag, Jensen, Lundahl, Sowter, etc. Tons of vintage options that are far better than the octal Altec stuff and far less $$$$$. Have fun.

I'd not use the Altec backwards at high level; not designed for the sort of level you'll want to see. Really not appropriate.

You'll probably find the 6SF5 to be noisy as first stage. If you stick with it, you'll want to by a half dozen and listen for lowest noise. You'd do much better with 6C5, IMO.

PP 6V6 is a lot of potential headroom, but is sort of wasted power and may be noisier than desired too. Maybe more to your needs if you lose the 6V6's and go with something like PP 6C5's driving a different output transformer. Something like the $12 Edcor XSM 15K:600 would work well.

Tons of options.

I doubt there's anything wrong with the Peavey.
Old 25th January 2009 | Show parent
  #3
Lives for gear
 
ulysses's Avatar
 
🎧 15 years
The Altec Peerless 4722 is really only suitable as an input transformer, because the turns ratio is too high to use it as an output transformer. You'll get 25dB of gain out of it as an input transformer (which is a lot - it's a rather high 1:18 ratio). As an output transformer, if you wired it backwards and strapped the "secondary" (really the primary) for a nominal 600ohms, you'd still have a 9:1 ratio. That wouldn't be appropriate for stepping down anything but a very large-amplitude, very high-impedance tube output. You'll lose about 19dB of gain in the process - most of what you gained with the input transformer. The similar-looking (but red) 15095 would be a better choice for the output transformer. Since you don't have one of those, I agree with emrr about using the value of these transformers to procure a preamp instead. If you are set on building something with them, your best bet would be a 2-channel preamp with these as input transformers.
The Bogen amp sounds like fun, but since it's a power amp, you'd be wasting a lot of chassis real estate and power supply capacity for just a mike preamp. You could do something else fun with it though, like play guitar through it. Likewise, the Dresden-Barnes power supply could be powering a 50W guitar amp (in fact, it could probably be made into a 50W guitar amp, since I would bet it currently uses power tubes as the pass devices). It's way overkill for a mike preamp.
As for the RCA tube manuals: Read them!
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