Phonoland

Ron\Rob: I'd like to start off by saying you both have been so helpful with working with me towards getting my jukebox issues resolved - and i am sure i speak for others you have helped as well. Its is much appreciated !!!!!!

Now to the good stuff, i have attached the full schematic in this post - it is 5 pages . Rob - i see where you reference CR102 on page 4 near the 5Y3GT Tube. At your recommendation Ron - i should replace this with the 1N4004 diode ?. I see Radio Shack still carries this and was wondering if i can use this (RadioShack (Catalog #: 2761103) 1N4004 Micro 1-Amp Diode - 30 amp surge. Type: 1N4004. Peak Inverse Voltage (PV): 400).
Can you also tell me which (if any) other diodes should be replaced with the 1N4004 - according to the schematic (page 2 parts list there are 4 0f them -> CR101 - CR104 ?

Thanks Guys !
Gary

Yep, those diodes are fine. Replace all of them.

Rob

They will work--for the dual diodes, I generally use 1N914 type signal diodes--but I use two in series to replace each half of the original diode. Some people like 3 in series -- I can't see any difference in operation-- Ron Rich

Okay, i will replace CR101 - CR104 each with a single 1N4004 then give it a try and post results .

Ok - here is where i am at, this amp has only two diodes, CR101 and CR102. I replaced the CR101(pic attached of old and replacement) and retested the amp - still not working. I took a look at the CR102 but have concerns (see picture) it is not the same as the CR101. I figured i'd get some input from you guys on this before going further - please take a look at both pics and you will see what i mean. Thanks -> Gary

CR102 PICTURE

Gary,
The "line mark" on the 1N4004 is the cathode side--same as the "+" mark on -02, or the "red dot" on -01.
I see at least 3 old caps there--that must be changed ! Also, if you have an AVCU installed in that amp, you have one dual anode diode in the AVC unit--Ron Rich

Thanks Ron - well i guess its time to replace the caps since none have been replaced yet. Who is a good source (at reasonable price) to get caps from ? I know there are some sellers out there that sell kits but they typically run you more money because they package them. What are your suggestions as far as which caps to replace and should i buy them individually \kit - and from who ?
Thx again.

Gary,
IMHO, replacing caps is the first thing you should have done ! Next check resistors for spec. and replace any that are out of spec. I had (incorrectly) somehow, ASSUMED you had done so already !
Doing amps, I usually have most of the caps needed in stock--if not, I go to one of the cap kit sellers listed above in this section--all have seemed "fair" to me--price wise-- Ron Rich

I will order the cap kit and install it - thanks !

One other question with regards to the testing with the line level source to determine if the transistor was cutting off due to low voltage. (original post by Rob is below)

When i did this test i had very low sound (music) over the speakers. Does that mean that the transistors are good ?

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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.
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At this point, I would say that the test done is not valid, due to the other problems exhibited here----If you got good sound, I would guess the transistor, or it's circuitry, was defective---Ron Rich

Okay - thanks - i will order the cap kit and install it.