Seeburg USC-2 w/ TSA 10 code B amp.

Ron, they are diodes. They were popular in bias stabilization circuits in the late 60's on through the 80's. they supposedly are an improvement over the practice of just stringing two or three regular diodes in series on a heatsink for bias control.

I'm not sure what they bring to the AGC circuit and haven't had any fail..yet. However, if you suggest doing so, I'll make a note to replace them with the three per leg diode strings I use in the AGC circuits.

Rob

Hi Rob, Ron
I tacked the resistors to the RCA connectors, plugged in an MP3 player to the input RCA's on the amp and I got music!! It was heavy on the bass, and the right channel wasn't the same volume (a little less) as the left, but there was NO distortion or "noise". The stabistor is in the center of the board under a shield or heat sink. Does this mean that the AMP is OK, and the problems are with the phono cart.?
Thanks,
Steve K.

Rob,
Those were actually two diodes in series, in one package-- Seeburg ran into a "flock" of them that were intermittently either opening, or closing, don't recall which--(gotta note on it somewhere, 'splaining on how to build a "stress tester", for them ?) for milliseconds. On the older red/yellow sel. packages, I have used both two and three silicon diodes, in series, to replace them--can't detect any difference between 2, or 3 ? Ron Rich

Steve,
I would guess that the amp is OK--
Either you have a bad cart--like I said--only saw one, new, bad cart. in my life, or problems with the wiring to it ?
I have seen carts that "someone" has bent one or more of the pins that connect to the socket--these have broken the connection to the coil--but that's usually obvious.-- BTW The "thing" under the metal clip on the AVC board is the "choke"--not a stabistor-- Ron Rich

Ron,
I'll check continuity on the wires from the socket to the terminal strip next but I'm still not getting any resistance on one of the channels at the cartridge itself?
Steve K.

Steve,
That would indicate a bad cartridge--?
Ron Rich

Hi Rob, Ron,
I ordered a replacement cartridge this morning from Steve at Victory Glass and hopefully that will make things better in the USC-2. Will let you know what happens when it gets here. It gives me some time for "cosmetic" work......

Thanks,
Steve K.

SmyrnaSteve wrote:Hi Rob, Ron
I tacked the resistors to the RCA connectors, plugged in an MP3 player to the input RCA's on the amp and I got music!! It was heavy on the bass, and the right channel wasn't the same volume (a little less) as the left, but there was NO distortion or "noise". The stabistor is in the center of the board under a shield or heat sink. Does this mean that the AMP is OK, and the problems are with the phono cart.?
Thanks,
Steve K.

Steve, as for the imbalance, this can be a number of things.

-Balance control not centered.
-Amp un-rebuilt.
-Defective diodes in the AGC providing uneven attenuation of loud disks.
-Mistracking volume pot tapers. This is fairly common and channels will often have a differential of up to 2db at various points on the control.

If the amp hasn't been rebuilt there is not much point in going further 'till that is done. You'll find most of these sorts of problems go away with fresh capacitors.

To test whether it is the pot or amp circuit. Strap the inputs together for an absolute mono signal. Set volume control to max. make sure them has a load of either identical speakers ot resistors (20 watt or more @4-8 ohms). Connect either a signal generator, or other device is preferable with a constant tone signal and use only enough level from it to get audio from the amp. If speakers are used you can just listen dead center. If you have a meter with DB scale compare the two channels.

If you connect a Vom or multimeter with AC scale across both channels, there should be almost no reading as compared to the reading of each channel separately. This is a revealing test because if the channels are perfectly balanced (rarely possible) there would be no AC reading, so the degree in which they differ is reflected in the higher the reading is on the meter.

When I do these tests I ground out the AGC voltage to eliminate it from affecting teh results. That voltage is on the 100mfd capacitor on the AGC -SOS board above the two preamp-drivers. It should also appear on this pin of the Mech socket on the amp:
http://s1192.photobucket.com/user/Rob-N ... rt=2&o=195 It is the lower left pin.

One advantage of grounding out the AGC is that it permits you to inject a bit more level and thus track the balance of the volume control taper.

The idea is to determine whether any imbalance occurs before the volume control -or after.

Rob