Seeburg Amp Rebuild

OK, so thanks to the folks here (shout out to Rob NYC and Ron) I've got my Seeburg LS3 up and running. But as we know, projects like this are never 'done'. Now I'd like to improve the sound quality.

The sound always is a bit 'muted' sounding unless you really crank it up. Maybe they were intended this way, but at lower volumes I dont have the treble I'd like.

The amp has bass/treble switches but these do absolutely nothing to change the sound. Putting these two things together (plus the fact it was previously owned by somoene who never did any maintenance), I'm assuming the amp is probably due for some work.

So, here's my questions:

1. Should I buy the SHP Amp book if I really dont know a TON about amps and dont have any specialized tools? Is it written for someone like me (who works on stuff until he understands it but has no background in electrical engineering) or is it written assuming you already know how these things work?

2. I've rebuilt arcade monitors, so I can certainly recap PCBs and replace components. Is this all it takes to rebuild an amp like this or do you need special tools/skills specific to these amps?

3. Worse comes to worse, can anyone recommend someone in the Michigan area who would do a rebuild and give me a general ballpark of cost?

Essentially I'm interested in going in this direction next and am weighing my options.

Thanks everyone, enjoying these forums!

Rob,
The late Tony Miller's SHP book is written in technical terms. Tony was an engineer, and we used to laugh about it whenever we got together--He would "confuse me", and I would always retort--"PLEASE--speak 'hood"--to which he would usually reply--"I AM speaking, MY, 'hood".
You should NOT have a SHP type amp in that phonograph ! It should have a TSA-8 in it.
If you do, I would suggest that you find someone who is very familiar with, ALL "versions" of them, to rebuild it properly. These can be "tricky"--I have done several hundred of them--if you wish to send it to me, please PM me.
Ron Rich

woah! Good to know that's even the wrong amp!!!! From the description I thought it was the same amp in all these seeburgs.

Is there a book on the TSA-8?

Rob,
What kin I said--"RTFM" ??
P.S.Which "SHP" is installed--which volume control is being used ? How are the speakers connected ??
Ron Rich

Ron Rich wrote:Rob,
What kin I said--"RTFM" ??
P.S.Which "SHP" is installed--which volume control is being used ? How are the speakers connected ??
Ron Rich

Ok Ok...RTFM

I don't think a SHP is installed...I think it is the TSA-8, I just was reading the description of the SHP manual and thought it implied that's the amp in all of these.

So before I post more, I should pull out my freakin' manual and give it a read

At the very least I'm thinking I should start looking for a place to buy a cap kit as it almost certainly will be a good place to start.

Rob,
Pull out the amplifier also--and READ the type number, of what ever amp happens to be installed in your phonograph --
I purchase kits from verntisdale ( listed above, in "stickies").
BTW--you did not answer me about speaker hookups ?? Ron Rich

Rob, Ron's advice to rebuild the amp is "right-on". However, it is also possible that the amp is not "un-squelching" in play mode due to dirty or mis-formed contacts.

This will cause the amp to have very low level and thus require a high volume pot setting which removes the bass boost control altogether. It would not explain the absence of treble control operation. Have you checked that the tweeters, such as they are, are working? If those are dead they'll be no way to tell if the treble control is actually working unless you hook up an external speaker.

On the mute relay the squelch contacts is the center-upper center one that make when the relay falls out. Look at the schematic and you'll see that the top-center contact is grounded in play mode. This grounds-out the AGC squelch bias and simultaneously allows the AGC source diodes to derive control voltage from the audio signal.

My point here is that on an amp this old it is likely that there is more than one fault present. This is why i always went to a complete rebuild and bench test before bothering to re-assemble the machine. It does take away some of the fun and drama of the first power-up, but there are far fewer little-s--ts (as Nixon called them) to deal with later.

Rob/NYC

Just had the amp out and it is indeed an TSA8, so that clears that up.

Ron Rich wrote:BTW--you did not answer me about speaker hookups ?? Ron Rich

Sorry, I thought that may have been an SHP-specific question. The attached image should give you what you need to know, I believe...



Rob: I hear ya about a total rebuild. As I mentioned when PMing with Ron about a rebuild, the problem is cost. I only paid $300 for this juke and I dont really want to pour a bunch of money into it...a full rebuild is probably going to cost me what I paid for the box to begin with

I know you guys would cringe, but my thinking may end up being that me doing what I can (ie. recapping for example) may be better than doing nothing...or maybe not. I donno. Not totally committed do doing anything yet, just gathering info on the possibilities.

Rob,
Looks as if the "scratch compensator" is set above min--change it to min., to obtain more treble--
Also be sure black wire is on G, not blue wire ( sometimes they are difficult to tell apart--can't from photo)
If you still don't have enough treble--suspect inferior needles--
Ron Rich

Ron Rich wrote:Rob,
Looks as if the "scratch compensator" is set above min--change it to min., to obtain more treble--
Also be sure black wire is on G, not blue wire ( sometimes they are difficult to tell apart--can't from photo)
If you still don't have enough treble--suspect inferior needles--
Ron Rich

Yeah, honestly it didn't seem like the scratch compensator does anything either...but I'll switch it anyway and see if I notice a difference. I also just put new needles on...

Rob, one test is to connect a decent external speaker to the amp (disconnect the internals by removing the two top wires) and see how it sounds. Use a speaker with decent high end. A raw driver (no enclosure) with a whizzer cone is fine here, Try one channel, turn volume all the way down, change the top connection (bottom common can stay the same) and switch to the other channel. If the sound is good now, you'll need to investigate the speaker system.

On amp rebuilding. after seeing your pic I have a few points. those amps use a combination of printed boards and point-to-point. they are very easy to rebuild, BUT there are two main pitfalls you need know about.

Here is a pic of a TSA-7 removed earlier this year after 18 years on-location.
http://s1192.photobucket.com/user/Rob-N ... ort=2&o=77
It was removed due to AGC failure. This was caused by the slide-through connectors that couple the lower preamp-tone boards to the AGC board on top of them.

On these amps it is the edge and through-hole connections that fail over time due to oxidation.

Another, more important problem area is the bias pots on each preamp-tone board. These develop dead spots due again to oxidation and dirt. If they lose connection it will kill the output transistors of the affected channel instantly. Unfortunately I can't show them on that pic as I removed and replaced them with fixed resistors long ago. The new resistor is near the edge connector on the under-boards close to the R5121 stencil. I used 100 ohm 'cause I had them handy although 110-120 might be better.

So, if you do decide to rebuild the amp yourself make sure the boards are cleaned along with the edge connectors and caution when powering it up. i use a variac and meter the emitter current on the output transistors. However a small wattage light bulb in series with the power cord might be adequate too.

You can do this work yourself, just be aware of the problem areas.

Rob

Really excellent stuff here, Rob, thanks. I only understood half of it but its one of those posts I'll go back to over and over as I learn more. Good general info here.

Thanks for taking the time!

Just a quick update: I got my recap kit from Jukebox Friday Night and completed the recap (along wtih through-post and edge connector cleaning) last night. What a HUGE difference in sound quality! I suddenly have treble again

For any noobs that stumble across this, I want to reassure you it's not as hard as it sounds in some of these posts. I'm learning more and more that 'a recap is a recap' so if you've done one, you can do pretty much any other.

I have to say I wasn't thrilled with the price I paid for the cap kit from Jukebox Friday Night, though. I know he says they're top quality caps, so maybe the cost really adds up, but I paid over $30 for what totaled probably 15 caps. It seems that even good caps from Mouser shouldn't add up to this much...but I must admit the convenience of 'one click' cap kits might be worth the extra money.

Either way, recapped and all set! In the coming weeks I'll be thinking about learning how to properly bias it (I think it's good now, and I've RTFM'd, but I will try to adjust that soon) and fix some microlog issues I'm having...but those will be different posts.

For now, I'm recapped and sounding much better. Thanks to Rob and Ron for all the help and encouragement. I would never have gotten very far with this Juke without their generous help and advice.

Rob,
Word of advise--don't attempt to "fix whut ain't broke"--leave the bias pots alone--especially if still sealed, and you have not changed any components, other than caps--Ron Rich

Thanks Ron, that was actually my inclination....I kept reading how 'if you change any components on the amp boards it should be re-biased', but I know that (often times) doesn't include a recap. I haven't changed out any transistors or anything else, so if you say "leave it as is" that's what I'll do.