Phonoland

Assuming this is a SHFA-5 removing the mute plug during play should result in volume going up unless you are playing a -very- loud record. It should not "fade".

Typical operation of the tube amps post K models is that during rest-scan and changing a squelch voltage is applied from the 25vac in the mech through voltage divider resistor in the mech to mute plug (pin 3 here) to the AGC rectifiers where it becomes a DC and applied to the time constant (C143) causing heavy conduction in the control diodes (CR 103-104) this is equivalent to the attenuation during a very loud record.

During play the contacts in the mech close and short the 25vac to ground killing squelch and at the same time allowing a ground point for the diodes in CR102 to generate the AGC control voltage to bias the AGC diodes (CR 103-104).

So, checking what is going on at Pin 3 of the mute plug might be interesting.

During rest-scan there should be low AC there.

In play mode no voltage.

At C143:

At rest-scan a constant low DC.

In play a varying DC depending on record and NO voltage (a few mv's is ok).

Rob

Darrell,
If I understand correctly--I would guess that you have a problem in the mute plug itself ?
Pop the cap off and check that plug---Also, you might check the input plug, ground pin--
SHFA-4 and 5's have no "speaker plugs"--they both have a "terminal strip for speakers ?? Ron Rich

Ron & Rob

Thank you very much for all the excellent ideas. When I messed around with the mute plug last night I decided to use Deoxit on the plug and plug socket. The problem is now non existent, so I believe the problem is/was in the plug/socket and if the problem returns I will then do the other things you have mentioned. The DS 100 has now played for several hours(while being turned off and on several times) without any loss oof sound!

Best
Darrell

Darrell,
That would indicate that you were loosing the ground connection--I would remove that plug, and use "Krokus" cloth on all the pins. Ron Rich

Ron

I will do that, thank you.

Best
Darrell

Oh no! The exact same problem has beset me again after 3 months of working fine I guess it is now time to tear the plug apart and examine that as the first order of business.

On two of my model DS 160s I had this same rumble sound, a pop and loss of sound. The main difference in those two cases the sound would not return. With these two, it turned out that a resistor had failed. What are the odds that the same resistor in the DS 100 now losing sound is slowly failing and that is why it will play for a while and then lose sound?

Best
Darrell

Darrell,
Probably pretty high--all the resistors are the same age, and probably brand--Which resistor failed, in what circuit--?? Ron Rich

Ron

It is a 7 watt 100 ohm resistor R-129 on the schematic, however, now that I think about it I do not think that is the problem. I remember I switched a known good amp with this amp and the trouble stayed with the box and did not go with the amp, indicating that the problem was not any part go the amp.

So back to the drawing board and a through search of the connections between the amp and the rest of the jukebox, starting with the audio and mute plugs, which I have already used detoxit and crocus cloth on.

Best
Darrell

Hi Darrell,
I have replaced a number of those resistors--they do "go bad" ( I use a 10 watt replacement).
Also check the "squelch contacts" on the mech--
Ron Rich