[FONT="]

INFO:

Power Xfmr – P-TF22798

Output Xfmr – P-TF 22848 – 4 ohms

Choke – 22699

Oscilloscope probe X1

**No**Sinewave input:

Power input – (119.5 Vac)

PT xfmr output – (350 Vac)

Standby on B+ – (+490 Vdc)

Standby off B+ - (+435 Vdc)

2- 6L6GC Outputs

Output xfmr CT – (+435 Vdc)

Output tube Plates – (+433 Vdc)

Output tube Screens – (+434 Vdc)

Output tube Cathodes I – (48.4 ma)

Output tube Grids – (-40 Vdc)

Phase Inverter 12AT7

PI-2 – (+63 Vdc)

PI-3 – (+98 Vdc)

PI-7 – (+65.2 Vdc)

PI-1 – (+226 Vdc)

PI-6 – (+226.7 Vdc)

V at junction of 82k/100k – (+423 Vdc)

Signal

**Applied**to preamp input: 200 mv.

PI-2 – (+61.6 Vdc)

PI-2 – (6 Vpk-pk)

PI-7 – (+63.8Vdc)

PI-7 – (5 Vpk-pk)

PI-1 – (+215 Vdc)

PI-1 – (45 Vpk-pk)

PI-6 – (+215 Vdc)

PI-6 – (45 Vpk-pk)

1-6L6G –5 – (-40.3 Vdc)

1-6L6G –5 – (45 Vpk-pk)

1-6L6G –3 – (+410 Vdc)

1-6L6G –3 – ( HUGE Vpk-pk)

2-6L6G –5 – (-39.8 Vdc)

2-6L6G –5 – (45 Vpk-pk)

2-6L6G –3 – (+407 Vdc)

2-6L6G –3 – ( HUGE Vpk-pk)

With only a 1X probe I could not measure the Vpk-pk on pin 3 of the output tubes but it was way over 45 Vpk-pk. I think I might be able to use a 10meg resistor in series with the probe and measure it as a 10X. I have a 1/10/20/100X probe on the way.

OUTPUT SIGNAL at Speaker Jack: ( 45 Vpk-pk)

I was using a 8 ohm passive load on the 4 ohm output so I would expect the output to be lower. So, is 45 Vpk-pk correct with this load? I have two output jacks wired in parallel so I can install two 8 ohm speakers. I went back and installed another 8 ohm passive load which gave me 4 ohms. Here are my calculations as to what the Power Output should be with both 8 ohm and 4 ohm:

Vrms = .3535 x Vpk-pk

Vrms = .3535 x 45

Vrms = 15.90

__8 ohm load calculation:__

P = Vrms2/R

P = 15.90 x 15.90 = 252.81/ 8

P = 31.60 W

I was thinking that I could get at least 40Ws out of this amp but the calculations don't give me that amount.

Outputs biased at 70%

Plate voltage 433 Vdc

Tubes 30W

.70 X 30 = 21

21 / 433000 = 48.4 ma

__4 ohm load calculation:__

P = Vrms2/R

P = 15.90 x 15.90 = 252.81/ 4

P = 62.20 W

The 4 ohm calculation just don’t seem right to me and I think I’m missing something in my way of thinking especially since the tubes should not be able to produce more than the 30W each since they are biased at 70%. When I went from 8 ohms to 4 ohms, the output sinewave did not increase so I used the same Vpk-pk to recalculate the Power Output with a 4 ohm load. Help… straighten me out!!

[/FONT]