2330 has me stumped

Jailtime

Standin' on a corner
I'm working on a 2330 that had been previously hacked up. As a baseline, it did work and had acceptable DC offset after I repaired the preamp that was missing parts.

I rebuilt the amplifiers and part of the power supply today. Previous tech had installed MJE15030 transistors, a new relay, and some of the caps on the power supply. I finished that up, and put new caps, trimmers, diff pairs, and Q703/724/725 in the amplifiers. I used KSC1845 for diff pairs/Q703 (2SC1775), and KSC945C/KSA733C for Q724/725 (2SC945/2SA733).

I ran it up on a DBT (100W bulb) to get a ballpark on bias and offset, I was able to tweak bias in at 10mV, low but I like to be safe on the DBT. It did take a while to come out of protect, DC offset was 110mV on each channel. Tried to tweak it on the left, it would come down for a few seconds, then rise back up to 110mV (best I could do). Tried the right, same results, but it was a bit more unstable and tripped the relay. It hasn't come out of protect since.

Now both amps are showing around that 110mV offset on the pins before the relay, and both have bias of 37mV (!) which will not adjust, still on the DBT. They also pull down the 35V from the power supply, one amp will pull it down to about 26, both pull it down to 18. The power supply makes a stable 35V with the amps unplugged.
 
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could be hi-freq osc. check with scope. new transistors might be too fast, can be compensated with small caps,

do the transistors get hot?
 
Never had a problem with the KSC/KSA parts before, that would be strange. Transistors don't get hot, but it's been on the DBT to limit possible damage.
 
Yet another lesson in KISS for me. Turned out to be the grounds. I really need to make a habit of checking and cleaning all of those ground points in this old gear.

Now on to fixing the tuner in this beast, no FM stereo and FM tuning meter is dead.
 
And look at this middle finger coming at us from the upper right corner: LINK
November 2014. It does pay to read the data sheet, instead of
looking at the pretty picture that says, 1. Emitter 2. Base 3. Collector
Off to the left are some words too,
* Suffix "-C" [look at that, they even put the hyphen
in there just in case guys like me saw that it was
missing and it might mean something different.]
means Center Collector (1. Emitter 2. Collector 3. Base)

They used to have words of warning in the Corps,
something like if there is a discrepancy between the
picture and the written text, the text take precedence.

Now I know why they made us read.
 
Jailtime and others.

Hopefully posting this will prevent other folks from having the same "challenge".

Enjoy.

KSC945-C USMC_SPIKE.jpg

KSC945-C USMC_SPIKE.jpg
 
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