Hartke GT100 power amp section schematic needed....

[km6xz]

I got a GT100 that had been "repaired" by someone who thought the best way was to modify everything. I want to put it back to stock. I have the schematic of the preamp section and got it back to stock. I need to replace most parts in the power amp section with the original values so would really appreciate someone pointing the way to a power amp schematic.

[Steve L]

Hartke GT100 Schematics

Here it is, page 2.

Hartke GT100 Schematics.pdf

Steve

[g1]

Once it's done, I'd be interested to know if you get a glitch into a 4 ohm resistive load. One I worked on had the top alternation flatten off a bit sooner than the bottom into 4 ohms, but not 8. Q7 was kicking in early, disabling it (or freezing it) cured the glitch. I tried replacing pretty much everything to no avail. So I had to let it go with the glitch and thought it may have been a design issue.

[km6xz]

Thank you very much Steve.
Right now, the unit has full DC offset at the outputs but a basic test of active devices has not revealed a cause. Now I should be able to get it back on stock condition, and working. The preamp had a number of broken traces, one channel out and about a dozen questionable mods.

g-gone, I will be sure to check it on 4 ohms. The speakers in the combo are in parallel, 16 ohms except so it probably maybe the real design intent was 8 ohms.

[g1]

Thanks, are they the stock (GXL12 75 watt) speakers? Is there an ext. spkr jack? The unit I worked on was a head. It had 2 spkr jacks labelled minimum 4 ohm total load.
I don't think the combo would put out 100W into 8 ohms. But you are probably right, may have been really designed for 8 ohm load.

[km6xz]

These are stock 12's in the combo which has no speaker jacks. It does generate 30vrms into 8 ohms. based on the circuit, I would be surprised if it could source enough current for a lower z load. There are only two devices per rail of 55volts so at 4 ohms would be right at the D718/B688 SOA. Anyway, current starving is not a problem on the bench with 8 ohms on this one.
I replaced all the parts that were switched, bridges the cut traces, and made a couple close approximations in substitutions and it is working well now. I was at it until 4:40 this morning.
The original complaint was to make it sound better. It had just been worked on by a home shop that apparently did not know how to fix it so redesigned it and added lots of wholesale circuit changes, and added parallel reversed LEDs in every feedback loop. It had great HF oscillation in the pre, would not switch channels and the power amp was full offset to the positive rail. Other than that, he got a "great" deal in it only costing him $140 from the other amateur shop to ruin his amp. I am only charging him 2000 rubles for saving it, that is $64. I guess I am too easy....

[Giulio]

Hello, I need complete schematic diagram GT100 but the "link" is not working, STEVE L or KM6XZ can you help me?
thanks

[Jazz P Bass]

Hartke GT100 Schematic

Here is the schematic.

[Giulio]

Here is the schematic.

JazzPBass
you are great and incredible. Many thanks and Merry Christmas

[AdrianM55]

Hello,

I know it’s an old post but I’ll give it a try regardless.
First post so I will introduce myself a bit my name is Adrian and im a guitar player and electronic hobbyst.

I recently acquired this amp and it wasn’t working... all mounting screws are missing along with two fuses and 12AX7.
I've ordered all them parts and installed them. Amp turns on but doesn’t produce any sound apart from constant buzz.

has anyone had something similar in their experience ? What is best way to start diagnosing this problem?
ive tried it with bulb and without and it makes same booing/buzzing noise whether there is a cable plugged it or not.

I hope I can resurrect some of the distant memories

thanks
Adrian

[Enzo]

Is there DC on the speaker?

[AdrianM55]

I’m just analysing schematics to try figure where is what.
What voltage should I be reading?

[AdrianM55]

I suspect that previous owner might have reversed blown fuse and installed it in the socked for 110v.

I will check that voltage later on.
thanks

[Enzo]

Across the speaker we want to find ZERO volts DC, or at most a few millivolts.

[g1]

I suspect that previous owner might have reversed blown fuse and installed it in the socked for 110v.

So voltage is 240V in your country? And the previous owner installed fuseholder in 120V position then applied 240V to unit? It is then likely that some power supply components are damaged.

Schematic in post #8 above.