Seeburg Q160 with mono amp #C1HFA1 - Amp problems

Working on my Seeburg Q160 (mono amp #C1HFA1) - i have this one near completion. The juke mechanically works fine, but, the amplifier is dead (not rebuilt yet) so i am looking for some guidance with this to try and identify the problem and do the rebuild myself - the amp itself looks pretty simple in design and i am trying to save some cash by doing this one myself.
Here is what i have tested so far:
1 - i have two (not high end) tube testers (HeathKit TC-2 and Superior TV-11) and have tested all tubes on both testers - all test good.
2 - Tested Audio Output Transformer - Put the negative lead on the center tap of the primary, red wire. Measured to pin 9 of each 6973 plate and got 80 ohms and 105 ohms - should be around 100 ohms - not perfect but should be okay.
3 - Tested Filter Choke - 2 wires coming out of it, running between the 5Y3 and the filter caps - should be 50 ohms, got 60 ohms - should be okay.

Looking for next steps and suggestions on how to proceed.

Thanks All !!

Got the schematic--or, at least a SHFA-1 schematic (as that amp is almost identical to half a SHFA-1). ??
Volume control and speaker plug ( with B+ jumper ) installed ? Squelch grounded as per service note ? At that point, trouble shoot as any amp---- Ron Rich

Yes - i have the schematic for the C1hfa1. I will check tonight.
Question, you mention the volume control and speaker plug (with B+ jumper) - i'm not familiar with the "B+ jumper", can you explain for me.
Also, the squelch (mute) ground - the schematic refers to pin 4 as ground - is this what you are referring to ?

Thanks again !

Check the schematic--it will show the speaker plug wiring--No B+, no workie !!
Mute is different from squelch--I do not have that schematic, but the wire going to the squelch contact (see mechanism schematic) needs to be grounded, when testing the amp.

gmendo wrote:Yes - i have the schematic for the C1hfa1. I will check tonight.
Question, you mention the volume control and speaker plug (with B+ jumper) - i'm not familiar with the "B+ jumper", can you explain for me.
Also, the squelch (mute) ground - the schematic refers to pin 4 as ground - is this what you are referring to ?

Thanks again !

On later tube models with a B+ jumper on the speaker plug it will look like this:

http://s1192.photobucket.com/user/Rob-N ... rt=2&o=221

The purpose was to kill the B+ if the speakers were not connected to load the output transformers. It runs from a the center tap of the high voltage winding to chassis ground. I usually just ran a permanent jumper to eliminate that as a source of trouble.

Two other causes for a 'dead" amp are poor connections at the volume control plug: In this case all tubes will be lit and rocking the plug may restore sound on one or both channels.

If either the amp tubes or rectifier tube heaters are not lit the Jones plug that connects the two units is the usual culprit.

Rob

Thanks Ron and Rob !!
I'll check this out tonight and we'll see what we come up with. Thanks again for the quick and detailed responses.
Gary

Okay - here is what i found:

- Mute\Squelch (5 pin conn - J103) has good ground to pins 2 and 4 (pic attached)
- Output\Speaker jack - j104 has B+ jumper (pic attached)
- Cleaned volume control plug connections and wiggled it when plugged in- no change.
- all tubes are lit, noticed though that the small 6BJ6 is slightly\dimly lit and not warm (normal ?) - did test on tube tester and checked okay.

So - looks like i am stuck here with at dead amp. I did take another Seeburg amp out of my other jukebox and put it in and it worked fine - just to rule everything else out.

I haven't done a full rebuild or component check yet (or ever done one on a tube amp) but am willing to try ( i do have digital and non-digital mulitmeters - looking for suggestions on what to check next ? I have attached the schematic as reference. Thanks for any help you can provide me !

Gary

Gary, you may as well start with B+ voltage checks. Start with Pin 8 off the 5Y3 at, or near 380VDC.

BTW: On your pic of the speaker plug, the red wire that goes to the orange-red wire is the one that must jump to chassis ground to establish B+.

Rob-NYC

Gary,
If "totally dead", check the voltages first, then the input transistor---If good, input signal as per the note on the schematic, and trace it thru the stages, till you find out where it's "lost"--Ron Rich

Rob,
Just saw your post--I think you are incorrect in stating that the red wire must jump, for B+ --- I believe the black wire, as shown, is correct--I think that Red and Yellow (normally blue--but Seeburg tended to run out of the correct colors, and sub anything they had), are the two "hot" outputs to the speakers ?? Ron Rich

Ron, take a look at this speaker harness from that era:
http://s1192.photobucket.com/user/Rob-N ... rt=2&o=221

Then look at the top schematic Gary posted. The jump is at the top.

I've long heard and read of Seeburg's money travails -I've never understood how a company that had a superior mech and selection system could always be on the skids.

I do think that eliminating the 200 was a mistake though.

Rob

Rob,
You are comparing apples to oranges here--Gary has a photo of the speaker JACK, you have a photo of the speaker PLUG.
Unfortunately back then when A-MP-loc connectors were first made, no pin designation numbers were on the housings. It appears to me that the connector Gary shows, is correct, as per the schematic--I assume that the plug also had a jumper on it, from your photo ?
Ron Rich

Thanks guys for the quick response !
I forgot to mention one other thing - when you turn the watts selector to "test" you get the loud annoying hum out of the speakers - thinking that the connectivity from the speaker output (with B+ jumper) to the speakers is good ?

I will do more testing tonight for voltages, etc. More to come .

Garry,
You are welcome--
RTFM --the speaker test does NOT indicate anything other than there is a low volt, AC supply, available, and if you can hear it, the speaker voice coil(s) is/are good. Ron Rich

Here is what i found from last night - I have attached a new picture of the speaker jack and plug, it does have the B+ jumper - and i have a good ground connection.

I did check the voltage on Pin 8 off the 5Y3. In standby, -.057 vdc. In scan\play i got 271.3 vdc. This is not near the 380 vdc - do you think this could be the problem or is this an acceptable voltage even though not near the 380 ?

Thanks