Picked up a Polytone 102A combo amp this morning

[tim]

Hey all...

Just picked up a Polytone amp at a yardsale this morning...$25...I couldn't pass it up. I plugged it in and it works, pots are a little scratchy but that's easily remedied.

I tried to Google the model number "102A" but nothing came up. Plenty of info on the "102" but it is a different animal than the "A" model. Is anyone familiar with this model?

I looked on the Polytone website but nada...

Thanks

[J M Fahey]

There shouldn't be a big difference, if any at all.
The entire Polytone line is based around a couple preamps and a couple power amps, mixed and matched in different ways and mostly varying speaker and cabinets.
Fine with me.
I bet it 99% matches the schematic you found with only mkinor differences.

[soundguruman]

I think 102A was a change in the output and driver devices.
It's the same amp with better transistors.

Polytone had repeat failures of transistors from heat, lack of thermal dissipation.
And the "A" model was an attempt to stop the overheating of the drivers and outputs.

A good sounding clean amp, with very poor thermal management, which was built in a garage.

Pretty much all original Polytones self destructed from heat. (self immolation)

[Chuck H]

Pretty much all original Polytones self destructed from heat. (self immolation)

Except this one.

[g1]

Yep. And all the other ones that are still around. Any that were destroyed, well I guess we wouldn't know about, except for folklore.

[J M Fahey]

More useless, made up "data", which somebody will believe and quote because
"he saw it in MEF".
Oh well, let's keep

[soundguruman]

Except this one.

You can still make a better heatsink for it. That's going to be the long term solution.

[Chuck H]

You can still make a better heatsink for it. That's going to be the long term solution.

I have no experience with these amps. If it's true they lack thermal stability I think a heat sink is sage advice.

[J M Fahey]

Don't remember if I ever repaired that exact model, but all which went through my bench did have good, finned heatsinks (good) inside a closed fiberglass stuffed cabinet (horrible).

So rather than "a better heatsink" which it already has, I'd at least open a couple vents, one near the "roof" and another near the "floor" so air at least can circulate.

I buy those generic circular, plastic vents sold for homemade speaker ports, the ones that are 2.5" nominal diameter and just 1" long, and also have a same size cup saw, and put both in the back panel (obviously cutting away fiberglass which would block said ports) so the job looks original, factory made, 2 small vents that seem to have been there from day 1.

That said, some users are superstitious like most Musicians and strongly object to my "mod" , using the old excuse "if it were actually necessary they would have already made it at the Factory" .

And truth is that unvented Polytones go on and on for ages.

[J M Fahey]

A gutshot showing the good heatsinks and the padded cell they are forced to live in:

[olddawg]

Don't remember if I ever repaired that exact model, but all which went through my bench did have good, finned heatsinks (good) inside a closed fiberglass stuffed cabinet (horrible).

So rather than "a better heatsink" which it already has, I'd at least open a couple vents, one near the "roof" and another near the "floor" so air at least can circulate.

I buy those generic circular, plastic vents sold for homemade speaker ports, the ones that are 2.5" nominal diameter and just 1" long, and also have a same size cup saw, and put both in the back panel (obviously cutting away fiberglass which would block said ports) so the job looks original, factory made, 2 small vents that seem to have been there from day 1.

That said, some users are superstitious like most Musicians and strongly object to my "mod" , using the old excuse "if it were actually necessary they would have already made it at the Factory" .

And truth is that unvented Polytones go on and on for ages.

Wouldn't porting it like that "detune" the cabinet? Or is it negligible in this case?

[52 Bill]

Wouldn't porting it like that "detune" the cabinet? Or is it negligible in this case?

These all have sealed cabinets, so it would probably change the tone.

I always thought that a heat sink that was mounted through the back panel would work well enough, like the later Roland cubes had. The cabinet could still be sealed if it was engineered correctly.

The 102 amps were older and had many different forms. Some had single speakers, some had multiple speakers, some had single channels and some had dual channels, but I think that they all had true vibrato and reverb.

For $25 bucks you got a great deal.

[J M Fahey]

Yes, it changed the tone somewhat.
It usually has a strong resonant peak at, say, 100 or 120 Hz, (the box is acoustically small for those speakers), which passes for "body" , the too small and short vents I added were not for actual tuning and what was heard was that the sound was a little less "boxy", never measured it but *very* probably that peak lost some "Q".
Nothing important anyway and no musician ever complained about that.
Those who did worried about "not being original anymore" which is a different thing.
Yes, I bet that if 2 same model were put side by side, only one vented, and somebody switched A/B for comparison, a difference would be noticed ..... but listening to the repaired amp 1 week later caused no concern.

Agree that the proper useful Mod would be to cut a rectangular window in the back, seal it with an oversized, putty sealed aluminum plate, mount the transistors on the inside (say, on an aluminum L bracket) and attach on the outside a flat backed finned heatsink such as this one:

which is exactly what I do in my compact Cube type amps.
Or in powered PA cabinets.
But usually nobody wanted that done to their Polytones, so plan B was discreet venting.
Which by the way looks factory original to people not familiar with that particular Polytone.

[tim]

Thanks all...I have been quite busy since yesterday so I haven't had a lot of time to do any research on this particular amp. This morning I did get a chance to look up the model 102 (no A) and it looks quite different...The 102 has the preamp and controls on the top rear where the "A" model has the controls on the front of the amp.

It has one channel (the space for the second channel is covered with a plastic plate) and then has vibrato and reverb controls as well. I haven't opened it up yet to see what it has for a speaker but I'm guessing by the size of the cab, it's probably a 15". I'll take a couple of pics in the next day or two so I can post them. Oddly, it also has four metal slider type feet on one side so it can flipped 90 degrees for some reason. Not sure what the thinking was to put those feet there.

I'm more interested in it's fair price value as I don't plan on keeping it. The last thing I need is another amp hanging around here. I don't want to give it away but I also don't want to try and get more than it's worth. If I can sell it for a few more bucks that I bought it for, that works for me.

I'm going to go through it and clean the pots and figure out what's up with the reverb. It doesn't seem to have the decay time I think it should...it's possible one of the springs is broken. The guy I bought it from lives here in town and he was playing his accordian through it for years. He hadn't played through for about ten years so he couldn't guarantee it worked or not...so I took a chance and paid the man.