Seeburg Q160 with mono amp #C1HFA1 - Amp problems

Gary,
Without the motor being turned on, you should have no B+, as it is dependent on the scan motor switches to light the filament on the rectifier tube (5Y3, in this case). The B+ being 100 volts too low IS a problem--but I don't know it's your only problem ? Ron Rich

Gary, normally that low B+ would at least get somewhat weak audio. Here because the transistor preamp derives it's voltages from that same source it is possible that the low voltage is letting the transistor go into cutoff.

At this point if you have another 5Y3 or a 5U4 -try that and check the voltages again.

To eliminate transistor cutoff as a possible cause of no sound, try putting a line-level source into the amp at the junction of R115 & Pin 7 of the 12AX7. You might also try that at Pin 7 of V104 -be prepared for audio that may be -loud- of it works.

Rob

Thanks Guys !
I do have a good working SHFA5 amp with a good 5U4-GB in it. Since the C1HFA1 calls for a 5Y3GT i just want to confirm i can try the 5U4 without damaging anything - please let me know, if it will work i will try it and retest the voltages.

Also, Rob - i'd like to try what you recommend - determine if the transistor is cutting off due to low voltage. I have attached pics of the test points. When you refer to "line-level source" - can you tell me how to do this ? Off the audio input jack ?

Thanks !!

Gary, a 5U4 will drop-in.

For signal injection I would just use a clip leads from the center of the RCA output from a tuner, CD, etc to Pin 7. I generally also use a capacitor in series to black any DC that might leak back into the player.n tube circuits anything 0.027 mfd or higher is fine.

rob

Excellent and thanks so much for helping me work through this - i will give this a try.
Gary

Rob, Okay - put the 5U4 in and got 331 vdc. Put the 5Y3 back in the hooked up line source to V102, totally dead. When hooked up to V104 i get a loud hum and can hear the music in the background (barely, very, very low).
Thanks
Gary

Gary,
My GUESS would be that you have wired in a new cap, "off" one terminal--or have installed the incorrect value cap somewhere ?? Ron Rich

OK, Gary, the reason you got a loud hum is that you didn't also connect the ground of the source you tried. I should have spelled that out as well. Just another case of me assuming something..I'll never be any good at this remote control troubleshootin' stuff

However, the fact of the loud hum serves the purpose anyway.

At this point I am in agreement with Ron (dammit--again!) that you've probably left off or miswired something during the rebuild. Go to the preamp and check for the minus 30V into R109. Since you are still a bit low with even with the 5U4 (leave it in for these tests) you can expect the -30 to be a bit low too though it should still work.

i think we're almost there...
Rob

Thanks again guys - my bad - i should have realized that the ground off the source had to be connected.
Checked voltage at R109, -21vdc, test point shown in attached pic.

- side note - i think i may have mentioned early on that there has been no rebuild or parts replacement on this amp yet - it is original and i was seeking help to narrow down the problem.. As always i appreciate your help with this and please let me know what you recommend next.

Thank you again Ron and Rob !
Gary

Gary,
OK--what should generate the 30 vdc on this amp ? If an old selenium rectum-fier, I would change it, and the AVC diode also--Both can be replaced by a 1N4004 diode. ( Red dot=cathode) Ron Rich

Good question on the -30vdc ... no reference to it on the schematic - i will have to look into it - thanks

Gary,
What is the page number on the schematic you are using--I'll climb up and get it down--(which WILL, cost you, dearly !! ) Ron Rich
Ron Rich

gmendo wrote:Good question on the -30vdc ... no reference to it on the schematic - i will have to look into it - thanks

Gary, if you look at the first schematic you posted you'll see that the LVDC comes off the diode right below the tube rectifier and through R153-C130.

This also points out something I had overlooked. On the amps using 6973 finals with fixed bias Seeburg also used that "C" supply to power the preamp as opposed to the older 6L6 amp where the preamp was powered through a voltage divider from the B+.
Not a big deal but worth mentioning to avoid confusion.

Rob

Ron Rich wrote:Gary,
What is the page number on the schematic you are using-- I'll climb up and get it down --(which WILL, cost you, dearly !! ) Ron Rich
Ron Rich

Don't you forget that back brace and walker, with the tennis balls on the legs and the little basket on the front.

Thanks, Mattie,
I do not have the walker--yet--coming very close to needing it though--I do have a cane, and use it daily, when we take our dog to the park--- as it's poorly maintained--full of "gopher holes", ad un-even ground. Ron Rich