I have this amplifier here now- 19 " rack model 6 " high,

5V4, 6BQ5 x 2, 12AX7 , 5879

Output trans. Triad 45448, Power Thoradson T-55815. Both beefy.

Its from biomed stuff, circa 50's.

Before I dig in has any one seen one before?

the 5979 was broken in socket, in its shield and I think it was because
of cold temps.

Made by Grass Instruments . Quincy.

New one on me, but if it was built for med specs, even in the 50's, it ought to be a better build than most. Good luck with it .

Larry

Looked at it today-

Output transformer primary :
to plates and screens-(with series 100 ohm.
one unused secondary wire, two grounded,
one to a feedback net.

Output jack has a series 'clipper switch'
appears to short out a pair of top hats
when on.

All carbon 1/2 watt 5 %

Input pentode heater DC , from
a FW selenium with 1000ufd.

Power transformer:
Has an unused (taped) CT wdg
Primary is 4 wire parallel ,
(220 volt possible)
Has a grounded shield wire.

Construction is terminal strip based.

Every solder joint has a dab of brown
inspection paint.

Lead dress is a big part of this amp.

Also, all the Sprague 0.1ceramics
have a flexible clear sleeve around them
and look like their wafers are visible and
bulky.

Wondering if the sleeve is to prevent the
caps from splitting apart

6BQ5- G1 series 1000 ohm,
cathode common bias 100
ohm/ 50 ufd.

Next task- Find the turns ratio of the
Triad transformer and see if it is
still good.

Is there possibly another number on the Triad output transformer, like maybe S-142A or S-144A ?
Ifso, specs are available.

--Chuck

grass instruments made high end stuff for medical use. they made lie detectors and other monitors.

Radiotech- Did you ever find more about this? I picked one up today & can't find much info. Is it meant for a speaker out?
Thanks

I did not find anything more, and the unit is still here. On my unit, the single 2 pin jack marked
OUT has a DC resistance of about 15 ohms which probably means the tap is set to an impedance
higher than a speaker.( perhaps a 25 or 70 volt line). It is all back together now waiting a tube. but
the transformer may have unused taps for 8 or 16 ohms.

What is the number and make of the output transformer on your unit ?

Triad 45448. I can't find in the catalogs. Power is Thordarson t-55952. I'll let you know if I find anything out. Looks like it could be turned into a good guitar amp .
Thanks

The number on the output transformer is the same here. I think the amp would do fine in a studio
as a monitor amp for mixing where the engineer wanted the hear a mix with tube sound on the speaker
end. I've never seen a guitar amp using small tubes with an opt this big and I think it would weird the
sound something fierce for those used to a Marshal or Fender.

Does yours look like this? Mine came with one of the two pin plugs shown.

Steve-
Mine looks similar but not rack mount. 10" long 5" deep. Looks hard to work in. Need to remove the 4 wirewounds to get to the tube sockets. I think I will just bring it up on a variac & cross my fingers. If it works and sounds good, great but not likely. Rather than repairing this tight thing, I would clear everything out and build from scratch using the chassis, PT, OT if appropriate and not fried by me & tubes. Something similar to a Vox AC 15 would be easy although tight. If the voltages are what I want, I think the huge iron would work fine for what I like in a guitar amp. I don't need sag or OT distortion like some prefer. May be tempted to put a VVR on the PI & Power tubes if I do a rebuild. It may be a while but I'll give you Transformer info if you don't beat me to it.
Scott

Mine seems to work fine. Amazing that these old caps seem ok. I put an 8 ohm speaker on the output and plugged a strat into the 1/4 inch jack which is connected to switch position 1 on this unit. Not sure if mine has been altered from the original since I got it at a flea mkt. & it has some sharpie labeling on the back. You should look at the grey input wiring on mine and see if it looks like yours.
Good Luck with yours
Scott