Traynor YGM-3 Dazed and Confused Input

[misterc57]

How did the guitar sound with input #1, still distorted? At what guitar volume level does it start to distort? What kind of pickups in guitar?
It's possible the amp is working fine, but this is all good experience for setting up the scope and power output measurement procedures anyway.
Agree with the others that direct into the scope with no probe is not a good idea for now.

Guitar is a dual humbucker stratocaster. Oddly input one is sounding fine now.

[misterc57]

Automatic Measurements: Period, frequency, cycle RMS, mean, peak-to-peak

You should be able to get on screen measurements of all the above, then save it as a preset. There will be a button or menu to let you choose between 50 ohm or 1 meg, but probably need the probe hooked in for that.

I def. want to see all that.

I have one probe. I've been scoping amp output at my dummy load box which has a BNC cable from the box to the scope. When I measure at the inputs or anywhere else I use my probe.

My dummy load box has a BNC output, 4/8 ohm switch, and an input jack (left to right).

[misterc57]

There should be a channel input settings menu - consult manual.



Using CH2 might show if CH1 is shot/out of calibration.

BTW, one of the most revealing amp tests is checking output power.
Takes 5 minutes if well prepared.

Here are my output power measurements. 13.7 VAC into 8 ohms = 23.5 watts RMS. Does this seem to high for two EL84?

1K cycles/second. Turned volume up until the sine wave started to distort, then backed off.

[Helmholtz]

Here are my output power measurements. 13.7 VAC into 8 ohms = 23.5 watts RMS. Does this seem to high for two EL84?

Yes, that seems insanely high, but possible with an irresponsible B+ of 400V. I expect short tube life.
BTW, from your scope display I estimate an output voltage of 38Vpp corresponding to 13.5Vrms, so pretty much in line with the DMM.

Apart from high supply voltage the amp seems to be fine.

[g1]

Yes, that seems insanely high, but possible with an irresponsible B+ of 400V. I expect short tube life.

These amps have been running on 400V B+ forever, and never seemed harder on power tubes than other amps. In my experience better tube life than a lot of other EL84 amps.
Not sure how they got away with it but they did. Maybe modern tubes are more problematic. The re-issues dropped B+ to around 370V.

misterc57 , are you sure your load is exactly 8 ohm? That will make a difference for the power calculation.

[misterc57]

My plates are 370V. My load is 8.1 ohms.

Reading the scope manual and took new readings.

13.55 VAC = 22.66 watts

[Helmholtz]

All fine,then.