Anyone with AMPEG V2 /V4 experience?

[pslebow]

So I'm inputting a more modest 80mV signal to guitar input since I was clearly driving preamp to cutoff. Strat with Texas Specials puts out more but its a nice safe level. Signal looks pretty good at all vol settings until I get to the grid of the 12AU7 inverter (V4 pin 2) - gets ugly just after 12 o'clock and really ugly beyond. Same for grids on the 7027 (pin 5 on V5 and V6). Note that the Strat gets ugly sounding around 9 o'clock - probably higher output than 80mV - Clearly not near maximum volume output when "clean". Is this how V2's/V4's behave?

Some pictures attached show what I see.

[Helmholtz]

Some pictures attached show what I see.

Looks all normal to me. Signal levels are huge and likely the amp reaches full (clean) output power at around "12 o'clock".

[pslebow]

Really appreciated the suggestions. I think it's artificially clean looking at 12 o'clock. I can't play clean on the guitar past 9 o'clock or 8:30. (off is at around 7 o'clock). It's also not a smooth transition to distorted - can hear it start to buzz around 9 o'clock with the guitar. I can measure the rms out into 8ohms but I would guess it's not going to be near the power for the two 7027's. I would think one should get "clean" power close to the rating for the V2. From comments here, it sounds like Ampeg designed for clean tones. I'd be interested to know where other V2/V4 owners see the clean/dirty transition.

[g1]

I'd be interested to know where other V2/V4 owners see the clean/dirty transition.

The reason I mentioned the sensitivity switch right off the bat was because I lent out my V4 to a friend and he returned it saying he couldn't get a clean tone. And he was a strat guy. He had it set at 0db sensitivity. I told him to try it at the -9db setting and turn down his guitar volume. Once he did that, it cleaned up.
Still gets to full power at around 10 o'clock on the amp volume control, depending on guitar output.
That is what matters, wherever gets you to full power.

Power tube grids will clip at peak voltage equal to the bias voltage. With around -60V bias, you will clip the grids at 120V p-p. And that should be about full power at the output.
The V amps can get a bit asymmetrical coming out of the PI because of the PI type (not LTPI).
You can use the ext.amp jack as an in or an out. So put a signal in there and see what the level is that gets just barely clipping at the grids.
Then put signal at the guitar input and see if you can set up for a clean signal up to that level, scoping at the ext. amp jack.

[pslebow]

Great info. Yes, my next test was to see how much clean power I really am getting. Can try the external amp input but I believe the signal was clean at that point which feeds the driver (half of V3) that feeds the inverter (V4). The inverter out is clean until 45v peak after which it brings in higher harmonics - pointy shape. ( I believe I measure 68V bias on power tube grids). Since people seem to feel my observed sag is reasonable, it doesn't sound like the electrolytics are terribly off.

[Helmholtz]

For comparison, the Fender Twin Reverb is known as a clean and loud amp.

Nevertheless audible distortion starts at a vol. setting around 4. But at that setting the amp is already very loud and puts out in excess of 80W at signal peaks (hard attack).

[pslebow]

Yes! My '69 Sup Rev starts breaking up at 3 and its LOUD. I reached out to a YouTuber familiar with the V series. He claims I should get full power undistorted until around 12 o'clock, I distort less than 9 o'clock. I will check to see if I get 50W clean, but I just by listening,I doubt it. I'm noticing some B+ voltages are off, 7027 plate voltages down by 35V - I suspect dropping resistors or maybe leaky filter cap.

[g1]

Yes! My '69 Sup Rev starts breaking up at 3 and its LOUD. I reached out to a YouTuber familiar with the V series. He claims I should get full power undistorted until around 12 o'clock, I distort less than 9 o'clock.

This will completely depend on his pickups and guitar volume setting. And the sensitivity switch (make sure it is working).

I will check to see if I get 50W clean, but I just by listening,I doubt it. I'm noticing some B+ voltages are off, 7027 plate voltages down by 35V - I suspect dropping resistors or maybe leaky filter cap.

Double check your bias voltage at pin5 of power tubes. Also check the power tube idle current if you have a means to do so. Too hot bias will pull down B+.
Leaky filter cap should show as excess ripple, check AC volts at power tube plates with no signal applied.

[pslebow]

They say "if it ain't broke..." but not sure if its broke! I get almost 20v rms into 8ohm OX load at 400 Hz (according to a curve I saw on web) which gives 50 W before distortion - the rated output for the V2 ! But can see cross-over notch. Measure B+ at 552 v vs. spec but there 444 V rms from PT. Where is the current going? Ripple is only 3 v rms on plates of 7027's. Waveform attached. Maybe I should tweak the bias resistor? Can't believe Mr. Clean Ampeg would design an amp to exceed undistorted output at such low volume settings.
Chasing my tail

[Helmholtz]

Can't believe Mr. Clean Ampeg would design an amp to exceed undistorted output at such low volume settings.

That just means the amp has more than ample gain.
With less gain vol.setting would have to be higher for same output.

What is the actual heater voltage?

[pslebow]

Yes, just odd that there would be so little to accommodate a high output pickup. Hardly any control with my single coil

Heater is 6.3 V so seems fine. Not sure if I should be seeing the crossover notch and the 40 v lower B+ than spec . Bias resistor is per spec. Output primary is 140 ohms/leg which I guess is reasonable.

Circuit board looks almost brand new, nothing changed, burnt or cracked.

Thanks y'all!

[g1]

Yes, just odd that there would be so little to accommodate a high output pickup. Hardly any control with my single coil

That is exactly what the sensitivity switch is there for. Maybe I'm flogging a dead horse, but since the very first response in the thread, you have yet to acknowledge that the switch even exists, never mind whether it is working right.

[pslebow]

Oh, I thought I had. Yes, the sensitivity rocker switch is set in least sensitive position. I'll keep sleuthing it....

[g1]

You had mentioned the resistance of the OT primary halves (140ohm/leg). Take exact measurements, then measure DC voltage (with no signal) across the same points. Calculate volts/ohm to see what the idle current is for each power tube. Post results.

[pslebow]

Will do.
Actually found Ampeg v2/V4 service manual.