by Rob-NYC »
Fri Feb 10, 2012 9:16 pm
On the Tormat, you should be able to use one from any of the early 160 models: 161-222-Q160-AY160 and of course DS160. Do ask if the Cinch-Jones plug is in good condition and that there are no broken pins.
The amp for that machine is an SHFA-5. This was Seeburg's last gasp tube amp. The amp itself has a more pure sound and fast (transient) than the earlier versions due to simpler signal path and no huge feedback loops in the tone circuit that produced big peaks and dips in the response. But as a result of that and the too-simple preamp they do sound a bit thin as compared to what tube machines normally sounded like.
In the two machines I worked-on w/these amps I bypassed the existing preamp and used an external which I slightly modded (not really necessary) the end result was better, more typical sound along with the benefit of the simpler circuits.
Minor problem areas:
The AGC diodes will have to be replaced for the channels to balance properly.
Looking at the schematic:
http://www.verntisdale.com/schem/shfa5.jpgCR102 Can be replaced with one silicon diode each
But for CR 103 and 104 you'll need to string 2 or three in series for each being replaced. this is due to the lower internal impedance of modern silicon diodes. I generally use 1N4001 or 1N4002 for all.
Decent 7199 tubes can be a problem and the volume control on those amps is high impedance and they can change in value to the point where there is a different curve on each channel.
Rob/NYC
"If we believe absurdities, we shall commit atrocities" -- Voltaire