4x6V6 output transformer

David Root · Post by **David Root** » Wed Mar 18, 2015 4:54 pm

+1 on the MM Jim Kelly OT. I used one in a "Double Deluxe", actually a doubled up De Armond R15, wonderful tone. Expensive though like all Mercury iron.

FWIW I also think the two Celestion Blues in that combo had a lot to do with the tone too!

FUCHSAUDIO · Post by **FUCHSAUDIO** » Thu Mar 19, 2015 6:31 pm

A dual 6L6 transformer is a darn near perfect match for 4 x 6V6's as well.

Garthhog · Post by **Garthhog** » Thu Mar 19, 2015 6:35 pm

Hammond 1650KA

turbo5speed · Post by **turbo5speed** » Thu Mar 19, 2015 10:44 pm

FUCHSAUDIO wrote:A dual 6L6 transformer is a darn near perfect match for 4 x 6V6's as well.

A dual 6L6 transformer?

matt h · Post by **matt h** » Thu Mar 19, 2015 11:04 pm

(deleted)

turbo5speed · Post by **turbo5speed** » Fri Mar 20, 2015 6:16 am

matt h wrote:dual 6L6= I think he means an OT intended for 2x 6L6 operation. (a push/pull OT like the ones used in bassmans, pros, supers, etc). Similarly, depending o your operating conditions, a lot of OTs intended for 2xEL34 or even 2xKT66 will work very, very well for a quad of 6v6's.

Yes, i am aware that any 2x6L6 OT is good for a quartet of 6V6's. Thx for the clarification because my head was about to explode on the thought of using 2 Ot's heheheh

turbo5speed · Post by **turbo5speed** » Fri Mar 20, 2015 6:42 am

Related to the same amp i need help from the gurus...

I installed a triode/pentode switch for high/low operation but the thingy is not working like i expected... i'll explain.

I wired a DPDT so that i can choose to connect the screen grid resistors either to the plates or to the normal screen grid supply. I am assuming that this is the correct way of doing things right?

The problem is when i switch the screen grid resistor to the plates (triode mode). I scopped the amp with a dummy load and, either i am having visions, or the amp goes past 100Watts???? With 4x6V6's??? I have 34V @ 1Khz in the 16 ohm tap wich gives me ((34^2/16)*sqr(2))= 101.8W????

Any idea of what i am doing wrong here? I checked the wiring a million times and all is good.

Thx.

sluckey · Post by **sluckey** » Fri Mar 20, 2015 12:30 pm

Is that 34V expressed as peak or peak to peak. Convert to RMS first, then plug the RMS value into the power formula.

34V peak = 24V RMS

34V peak to peak = 17V peak = 12V RMS

turbo5speed · Post by **turbo5speed** » Fri Mar 20, 2015 5:03 pm

sluckey wrote:Is that 34V expressed as peak or peak to peak. Convert to RMS first, then plug the RMS value into the power formula.

34V peak = 24V RMS

34V peak to peak = 17V peak = 12V RMS

mmmm... it's around 68V peak to peak with an oscilloscope and 34Vrms measured with a voltmeter.

sluckey · Post by **sluckey** » Fri Mar 20, 2015 5:11 pm

mmmm... it's around 68V peak to peak with an oscilloscope and 34Vrms measured with a voltmeter.

68v peak to peak has to be 34v peak.
RMS = .707PEAK = 24

Your scope and meter do not agree with each other.

turbo5speed · Post by **turbo5speed** » Fri Mar 20, 2015 6:40 pm

sluckey wrote:
mmmm... it's around 68V peak to peak with an oscilloscope and 34Vrms measured with a voltmeter.
68v peak to peak has to be 34v peak.
RMS = .707PEAK = 24

Your scope and meter do not agree with each other.

I was using my memory wich can be deceiving since it was 4am when i was doing the testing. Let me check everything again and get back to you. Appreciate the help.

My multimeter is not true rms by i am pretty sure i saw a 68 Vpp signal in the scope, and this was right before clipping.

turbo5speed · Post by **turbo5speed** » Fri Mar 27, 2015 1:36 am

sluckey wrote:
mmmm... it's around 68V peak to peak with an oscilloscope and 34Vrms measured with a voltmeter.
68v peak to peak has to be 34v peak.
RMS = .707PEAK = 24

Your scope and meter do not agree with each other.

Actually i believe the scope and the meter do agree with each other but in a different manner... i measured everything again.

Oscilloscopes read peak-to-peak ac signals. That beeing said, and using your own formula, if i have 68Vpp then i have 34Vp. RMS=34/sqr(2) or 34*0.707= 24Vrms

I have a 16 Ohm dummy load so it's 24^2/16=36Watts(rms) wich is ok for a quad of 6V6's. Before i was applying the wrong math but you made me see things correctly.

In triode mode the power goes down to around 55%, without much perceived change in volume but the amp sounds and feels different and clips much earlier of course.

But things get interesting on the power tubes. I measured the cathode current at full power in pentode mode (using the 1ohm bias resistors) and i see 66mA with 388Vdc in the plates... this gives me 25.6Watts plate dissipation

what am i missing here again?

Thx in advance.

turbo5speed · Post by **turbo5speed** » Sat Mar 28, 2015 12:03 pm

Anyone?

martin manning · Post by **martin manning** » Sat Mar 28, 2015 12:07 pm

How did you measure the voltage on the cathode current sense resistor? Using an oscilloscope would be best.

turbo5speed · Post by **turbo5speed** » Sat Mar 28, 2015 5:17 pm

martin manning wrote:How did you measure the voltage on the cathode current sense resistor? Using an oscilloscope would be best.

I used a digital multimeter, not sure i can trust the calibration on my poor old tektronix.

The Amp Garage

4x6V6 output transformer

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