Harmony H406 distorted Really low output

[freeformfx]

Safety first; remove the death cap across the line and fit a power lead with a ground.
Please confirm that alternative 'known good' speaker and tubes have been tried?
It may be helpful to undertake a voltage survey of the amp under static conditions and report the results, ie Vac / Vdc for all power supply caps and tube terminals.

I can do that , and already had a 3 prong prepared ready to go in this amp (it has a .01 death cap, wax kind too) so maybe i should do that first.
I just installed the old speaker from my Blues Deluxe (put in a texas heat) as my bench test speaker, for anything but twins and 100w marshall heads should be a good test speaker and I already think it was cleaner than this new texas heat. So I'm on a quick break from the shop.

[freeformfx]

got a 3 prong plug on it (sort of butchered the grommet hole argghh) got that death cap out which just snapped off at the cap as soon as I touched it. found a couple loose resistors going to the vibrato section, even though it was working, fixed those.
Now playing it through a proper bench speaker it sounds a little better ( i hope the original jensen is at least as good) and a bit more volume though it still doesn't sound more than 5 watts to me. Playing program music through it the freq response isn't too bad at about 1/4 to 1/2 volume. But plugging any instrument into it it breaks up past 1/4 volume. And it's a nice breakup too. I mean like a nice overdrive pedal. I wouldn't be shy to throw a mic on it the way it is and record a blistering solo. But I believe I'm missing some major db's.

I'll post some voltages. I thought the 6v6's (I have tried others) were biased too hot at 32ma maybe loosing some headroom/output but the math puts them at like 11.52 dissipation , I think. So that'd mean they're ok. I also wonder about my second dropping resistor being a 100k with 100k plate r's to V1 AND that the screens are so low maybe losing power too. But i think these voltages jive with what i read on another thread for this amp
v1 pin 1 125v
v1 pin 6 118v
v2 pin 1 199v
v2 pin 6 218v
v2 pin 8 I think is around 58v or so and the other preamp cathodes look normal
6v6's plates at 377 - 18v across cathode resistor
screens at 310

[MarkusBass]

These amps are very difficult to overdrive so I'm affraid that you won't be able to overdrive it when you fix it . You have to consider whether you want to fix it .

It seems to me that at the moment you actually don't know what is wrong with the amp. In order to find it out, you need to perform basic tests:
Test 1: switch it on and measure voltages on tubes. Put the voltages on the schematic and ask here if they are correct.
Test 2: provide a signal directly to the Volume pot. You will learn whether the problem is with the power amp, or with the preamp. Post results of the test here.

Mark

[freeformfx]

see post edit for some voltages. Yeah I'll try and inject a signal into the volume pot input and see what I get.
would those grid V2 pin 2 resistors (r15,16) being 470k instead of 220k cause volume drop? again I'm sure this was stock value, just not same as schem.

[MarkusBass]

v2 pin 8 I think is around 58v or so

I wonder what exactly means that "you think the voltage is 58V". Did you you measure it, or not?
If pin 8 of V2 is cathode, the voltage is definitely incorrect. It should be around 1,5 to 2V. Is the tube verified that it is good? Is grid connected to ground with Volume pot and grid resistor? I would say that the connection is broken, or the pot has failed, or you are testing the amp with a failed tube.
You can think of other problems (grid resistors, failed output transformer and so on) only when all other problems are solved. And here you have clearly completely incorrect voltage and you ignore it . Please check the voltage again and if it still 58V, find out why.

Mark

[pdf64]

These amps are very difficult to overdrive so I'm affraid that you won't be able to overdrive it when you fix it . You have to consider whether you want to fix it .

I don't see why that should be? OK gain is being dumped due to attenuation at the input and unbypassed cathodes, but a few minor mods should bring it close a 5E3 with 12AX7 in V1 slot.

would those grid V2 pin 2 resistors (r15,16) being 470k instead of 220k cause volume drop?

The difference probably only has a trivial effect on signal level.

[pdf64]

v1 pin 1 125v
v1 pin 6 118v
v2 pin 1 199v
v2 pin 6 218v
v2 pin 8 I think is around 58v or so and the other preamp cathodes look normal

Yes, they look reasonable, V2b is used as a cathodyne.

[MarkusBass]

Yes, they look reasonable, V2b is used as a cathodyne.

That's right. The schematic is hard to read and I haven't noticed that the V2b cathode resistor is 39k. So 58V seems to be correct.
What is left are the tests with signal.

[freeformfx]

That's right. The schematic is hard to read and I haven't noticed that the V2b cathode resistor is 39k. So 58V seems to be correct.
What is left are the tests with signal.

you want AC vltgs with a test tone running then?
the cathodes of V1 are about 1v
V2A cathode 1.7v
and I was wrong about V2B cathode it's more like 90vdc I wasn't familiar with a cathode being used that way.
Thanks

[MarkusBass]

Yes, but you need to specify both input and output signal. And by output signal I mean signal on anode of the tube. In this way you can calculate gain of the amp stage and verify whether it works correctly. For example, input signal: 100mV peak-peak, output: 6V peak-peak. The gain is 6V/0.1V = 60 - more or less correct.

Mark

[pdf64]

You'll need a suitable dummy load, or put the speaker in another room.

[freeformfx]

You'll need a suitable dummy load, or put the speaker in another room.

I'm deaf in one ear so what the hell I'll let it rip.
Ok putting a signal at the volume control has no difference I really notice between plugging in normally.
I injected a sine wave with an app into the second volume control and took AC readings using a scope and DMM. testing on the coupling caps feeding the 6v6's one side measures about .55vac and the side feeding the 6l6 grids reads 2.5vac with the volume dimed. It can be adjusted to zero with the volume pot.
pushing my phone's output hard enough though I could get up to about 4vac with the volume only 1/2 way up, and from there on up my meter would go into an infinity mode. (I''ve never seen that measuring vltg) Other ac vltgs I took seemed to be in that .5vac range iirc.
NOTE those diffences in AC don't show up on my scope, the wave looks the same whether it was .5v or 2.5v
well hope this gives an idea

[pdf64]

Deaf in one ear might encourage you to consider that what you've got remaining is all the more precious!

It may be that your meter can't cope with much Vac superimposed on Vdc.
Using a signal in the range 200- 400Hz, how big can the output voltage across the speaker get before the scope shows it rounding off?
With say 1Vac (in the above freq range) output to the speaker, can you use the scope to estimate the voltage (p-p or whatever) on the power tube plates; check both?

[freeformfx]

I'll try what you suggest even though i'm using a scope I don't really trust and am not much good with really but it does show waveforms semi properly at least.
But an old ROAD 1x15 bass amp just came up on my bench and i've already got it diagnosed so give me time to sort it out and I'll be back on that Harmony. I know that thing has balls in it somewhere. Other than just serving as a low volume saturated OD pedal. Although pretty sweet sounding.
I also own a silvertone 1482 2x6v6 which should be about the same wattage I'd say and it's got tons more headroom and volume

[freeformfx]

These amps are very difficult to overdrive so I'm affraid that you won't be able to overdrive it when you fix it . You have to consider whether you want to fix it .

Mark

Youre right really, I mean this thing is an overdrive machine really (running a strat , can't imagine what hb'rs sound like) It gets an early Black Crowes thing better than you've heard, rippin southern rock soloing, super crunchy chords, GnR... Sounds like a few watts honestly but actually sounds friggin amazing like this. Just to have to break out for that certain tone, ya know?