Harmony 575 solid state schematic

[loudthud]

I got cornered into attempting to repair a Harmony 575 solid state amp from about 1970. The thing is a nightmare inside, it's all built on terminal strips. Near as I can tell, the power supply is single rail, about 66V. There are 13 transistors that I can count and two more on insulated heat sinks. There is a 4 Amp fuse on B+ and another 4 Amp fuse in series with the speaker. Line fuse is 3 Amp. The power amp seems to work, about half the rail Voltage on the output cap. The complaint is No Sound. The input jacks on the front are the type where the ground is insulated from the chassis, same size threads as the Switchcraft jacks on a Fender amp, 3 of the 4 are broken. I have some similar ones in stock.

I can't find anything close schematic wise. Just found this ad.

[Enzo]

Probably not, but from here that amp head looks a bit like a Silvertone.

[loudthud]

Roughly the same size as the Silvertone, but deeper. Full size reverb pan, and get this: they used a 9 pin tube socket and shield for the tremolo bug. A photo cell is connected the pins 1 and 9 inside the shield. The top of the shield has a rubber grommet installed in the hole, and a #47 or similar bulb fills the hole in the grommet with a socket and lead wires attached.

My camera is out of commish, I'll try to get pics somehow.

Amp is about 40 inches high with speaker cabinet.

[vintagekiki]

Not Harmony 575 its Harmony H550 Solid State

https://www.youtube.com/watch?v=VpG4up8zPgk
1970 Harmony H550 Solid State
At 2:39 is located H550 schematic, little blurry, but it can be helpful.
At almost 60 minutes, can be found details in better resolution. Download with Print Scrn + Paint

Maybe this link be helpful
https://homerecording.com/bbs/threads/amp-schematics.229751/

I have the following schmeatics
HARMONY MODELS H-303A,H-304,H-304A, H-305, H-305A, H-306A, H-310, H-400A, H-410A, H-415, H-500,H-510,H-512
H-307X, H-311, H-322, H-420, H-430, H-440, H-515, H-525, H-535, H-545, H-570, H550

https://www.google.com/search?tbm=isch&q=Harmony+H550

[J M Fahey]

I got cornered into attempting to repair a Harmony 575 solid state amp from about 1970. The thing is a nightmare inside, it's all built on terminal strips.

Funny thing is, if it were a Tube amp,exact same situation would be described as: "The thing is Heaven inside, it's all built true point to point on terminal strips!!!!!! "

Not Harmony 575 its Harmony H550 Solid State

Thanks for finding it, but 550 is split supply, +/-38V and as generic as can be, including 2N3055 outputs.
While loudthud´s is:

Near as I can tell, the power supply is single rail, about 66V.

That said, it should be same level of complexity (meaning very simple) and preamps should be about same;power amp might still use driver transformer like many early Acoustic, VOX, Standel, etc.

If you take it easy, it should be very repairable; signal path is fully exposed so inject signal at inputs and follow it.
Once you lose it, either bad connections/wiring (the famous "loose cable" problem) or that stage will show wacky voltages.

[vintagekiki]

Except image from the catalog, it is not possible define which model it is.
I did not find any traces for H575 on search engine.
https://www.google.com/search?q=harmony+amplifier&tbm=isch ¹⁾

Exist H535, which matches as picture from catalog, but it is a tube amp.
https://reverb.com/item/5888360-harmony-535-50-watt-guitar-amp-head-1967

Maybe helpful to upload some images H575 (front panel, back panel, inside layout)

[loudthud]

The look from the front is very similar to the 535 vintagekiki posted above. The 575 even has a Standby switch which just disconnects the speaker. The reverb tank is fastened to the inside top of the case. The chassis is three sides of a rectangle cross-section with pieces of plywood forming the end pieces much like Valco or Supro amps of the same era. There may be a schematic glued to the reverb tank, I'll have to look.

I saw the video of the H550 vintagekiki linked above. Layout of that amp is totally different. The 575 has tube amp style 1-3/8 inch twist lock filter caps with phenolic mounting wafers. Two for the main filter separated by two 1 Ohm 5 Watt resistors connected in series to form a Pi CRC filter. A third cap is in series with the speaker. The caps are covered with cardboard tubes, can't see any markings. The power transformer is center tapped. There are two stud mount rectifier diodes that go to ground, the DC output comes off the center tap. The 575 does have the Gain switch like the H550. The output transistors are RCA 2N3772 that are mounted on extruded heatsinks. The driver transistors appear to be 2N2102 and 40362 in a quasi-complementary arrangement. No short circuit protection other than the fuses mentioned above.

The AC has been out at my shop. The thing has killed four hi-tech programmable thermostats. Now the guy installed an old style mechanical thermostat to see if it can stand the abuse.

[The Dude]

I repaired a similar model not too long ago. I don't think it was the exact model here. What I found was that several small electrolytic coupling caps were dead. I just ESR tested all of the caps in circuit and replaced any that read high ESR. After that, the amp was up and running.

[vintagekiki]

There may be a schematic glued to the reverb tank, I'll have to look.

If you find H575 shematic, please share with us.
I browsed Harmony-National-Supro-Valco portals there is nothing like H575.

Harmony-National-Supro-Valco schematic

https://el34world.com/charts/Schematics/files/Harmony/Harmony_Schematics.htm
https://www.schematicsunlimited.com/h/harmony
http://web.archive.org/web/20200206071349/http://harmony.demont.net/schematics.php
https://www.google.com/search?%20q=schematic%20&sitesearch=http%3A%2F%2Fharmony .demont.net%2F ¹⁾
http://web.archive.org/web/20200206090706/http://harmony.demont.net/amps.php
http://www.oldfrets.com/Valco/Schematics.html
https://www.schematicsunlimited.com/v/valco
https://el34world.com/charts/Schematics/Files/Valco/Valco_Schematics.htm
https://el34world.com/charts/Schematics/files/Supro/Supro_Schematics.htm
http://web.archive.org/web/20160317075119/http://www.valcoamp.com/schematics/valco_amps/#wpfb-cat-5

[loudthud]

Here are some pics from a friend's iphone. We found an old listing on Reverb, but I don't know how to search for old listings there.
The pots have date codes from 1967.

[J M Fahey]

Ouch!!!!!
Replacing parts with legs twisted around terminal holes, pressed tight with long nose pliers and then soldered is a royal PITA.

This amp brings old memories, my first tube amps were built exactly like that, including the U shaped aluminum chassis with hardwood ends and PTP on terminal strips but then I *quickly* bought the eyeletting press and started making "Fender type" boards (which I still use, 51 years later ).

Circuit must be relatively simple, but following paths along all those criscrossing wires with no logic must be a nightmare.

Fully restoring it will probably be a time black hole

[DrGonz78]

I worked on an old Gibson tube amp years ago that looked just like that layout. That was the amp where they had filled in the bottom of the cabinet with what looked like manure, logically to decouple the reverb tank from vibrations. It added a bit of labor to the repair. Thinking back on it, today I would have left the sh!t in there.

edit: just to clarify it wasn’t Gibson who had filled the bottom of cabinet with manure.

[vintagekiki]

We found an old listing on Reverb, but I don't know how to search for old listings there.

https://www.google.com/search?q=old+listing+on+Reverb

How do I find old Reverb listings?
You can utilize our search filter for Sold Listings to view previously sold listings on the site.
If you conduct a search on the site, you can filter via the Show Only field and select Sold Listings.

[loudthud]

Forgot to mention, no schematic on the reverb tank. The amp with it's 2x12 cabinet is about 52 inches tall. I looked through all the links in kiki's post #9 above, no luck finding the schematic.

Found this on Reverb, not exactly the same, but very close.

[loudthud]

Anyone know where to find Harmony catalogs online for free ? Looking for 1966 or 67.