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budmaestro 23rd June 2009 05:18 PM

Tubelab SSE measurements
I have been enjoying my simple se for over a year now and wanted to get some input as to what the "right" voltage measurements should be on this board(one amp is completed and gifted to my Dad last fathers day; the second board is still bread-boarded(sigh)).
This is what I get with my Fluke:
Yellow:1= 7.94 ac, 2= 5.95 ac
Green:1=3.42 ac, 2=3.42 ac
Blue(Edcor-plate):1=448 dc, 2=448 dc
Red(Edcor-B+):1=453 dc, 2=453 dc
@560 ohm resistor:1=36.3 dc, 2=34.1 dc
Choke Input: 478 dc
Primary Red:1=402 ac, 2=402.2 ac
Wall AC: 124.8 ac

I am using the Allied 6K7VG power transformer and the big Edcor CXSE25-8-5K
Current tubes are the 6P3cE (Russian 6L6GC)
Rectifier is a Hammond labeled british made GZ34
Driver is a RCA 12AT7WA
Choke is the recommended Triad
Motor run supplemental PS cap with film bypass
Currently running in Triode mode with no negative feedback
I have inrush current limiters (CL-90) on the primary(black) and center tap(red-yellow)

My question: shouldn't there be more difference between the plate and B
Also, why are the 5 volt filaments different?
Amp sounds good; these measurements have me puzzled.

Ty_Bower 23rd June 2009 05:53 PM

Re: Tubelab SSE measurements

Originally posted by budmaestro
My question: shouldn't there be more difference between the plate and B+?
Based on your measurements at the cathode resistor, you've got about 65 mA running through the tube (I=V/R). You indicate a ~5 volt drop across the output transformer's primary winding. This would suggest the primary has a DC resistance of ~80 ohms (R=V/I). That is a very reasonable value for a large output transformer.

By the way, 65 mA at 450 VDC is just under thirty watts. That's quite a bit more than the 6p3s-e can handle. It really should be kept under twenty watts. I'd recommend increasing the cathode resistance (try something around 800 ohms) or look for different output tube with a higher dissipation rating (maybe some EH KT88?)

oldmanStrat 23rd June 2009 08:33 PM


Also, why are the 5 volt filaments different?
Your power transformer should have 5vac and a 6.3vac filaments. So they will be different...

rknize 23rd June 2009 09:37 PM

I think he's asking why the 5V winding between the two amps is so different. One is 8V and one is 6V. 8V seems really this with the rectifier tube installed? Be careful, BTW, when checking the 5V filament when the rectifier is in there. Although there is only 5VAC across the winding, it will be full B+ (480VDC) with reference to ground (you).

I'm also confused about the 6.3V winding (green). Are you measuring this from the center tap? You should put the meter across the two solid green wires. Some meters don't do a very good job measuring AC, especially where there is a lot of noise on it, but the SSE doesn't rectify the 6.3VAC, so it should work fine.

oldmanStrat 23rd June 2009 09:56 PM

yup, my bad.

budmaestro 24th June 2009 03:14 AM

Yes, that is my biggest concern. Do I have a bad 5v winding? Should I fix it? Seems like it would be hard on the rectifier. Amp sounds great. Better than a couple $2000 amps I got sitting idle because I like the sound of this amp. I have another power tranny,same one. I'll swap them and check again. Weekend project.

rknize 24th June 2009 03:19 AM

I would be concerned about the nice NOS rectifier you are using being fed 8V. It will reduce the tubes life. However, based on your other measurements, I'm not sure if you meter is working very well at low AC voltages....

budmaestro 24th June 2009 11:23 PM

More measurements
:xeye:Red face here. I did more measurements going ACROSS the filament supply wires. Noob error, I was measuring to ground. So:
6.3v fil =6.7 volts AC
5.0v fil =5.24 volts AC
Per Ty's advice I pulled the 6P3C"s and installed my favorite tube in this amp, winged C KT-88's.
I'll get some bigger resistors to get the smaller tubes dialed in closer to 40-50 mA range.
Thanx for everyones help-back to musical enjoyment and a new chassis.
PS the KT-88's are running at 73 and 75 mA respectively

Ty_Bower 24th June 2009 11:41 PM

Re: More measurements

Originally posted by budmaestro
I pulled the 6P3C"s and installed my favorite tube in this amp, winged C KT-88's.
PS the KT-88's are running at 73 and 75 mA respectively

Sweet. I ran some New Sensor "Genalex" reissues in my Simple SE when I had 560 ohm resistors. KT88 are the bomb. Glad you sorted out the filament voltage confusion. :)

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