Stereomour voltage check not reading OK

[romanvm]

Hello Bottlehead community!

Received my stereomour about two weeks ago (first Bottlehead kit!) and after messing around with it and waiting for some missing parts I finally have it together.. Or so I thought lol

Resistance check passed just fine, all checked out at no more than 1-3%.

Voltage check is where I'm having problems. At the very first step it says to check in A1 and A4 it should read 2.5v, mine reads 1.2V (same on C1 & C4)  Tubes are not glowing.

I double and triple checked all my connections and everything seems good.. Of course I'm sure i missed something somewhere...

I just wanted to see what that 1.2V reading means and maybe one of you can point me to an area to look closely at. Also, fuse does not blow out.

Its wired it 4ohms.


Im sure i will feel dumb once problem is resolved lol but any help will be greatly appreciated...

[Doc B.]

That measurement is with your meter set to AC volts?

[romanvm]

Doc,

Yes it is.

Thanks

[Paul Birkeland]

Were you measuring with one probe on A1 and the other on A4?  My guess is that your black probe was grounded.

If all the DC voltages are OK, then look more carefully at your 2A3, it is glowing.

-PB

[romanvm]

PB,

I did measure it correctly, problem is that my DC voltages are not reading as they should also. I will measure it out and post results after work.

Thank you for your help.

Roman

[Doc B.]

Try measuring AC voltage across "start" and "finish" on the power supply PC board. It should read about 160VAC.

[Paul Birkeland]

I'd also recommend posting all of the DC voltages, that will give us a clear picture of what's going on.

-PB

[romanvm]

Doc,

I'm getting 80 VAC mesuring start and finish.. It seems as though AC & Doc voltages cut in half.

I'll post VDC readings tomorrow.

Thanks

[Paul Joppa]

Sounds like either the meter's battery is dead (check the power line voltage?) or you have a 240-v transformer instead of a 120-v one!

[Doc B.]

Yeah, that's where I was heading with the investigation. Sounds like we need to send you a 120V PT-6. Sorry for the error, not sure what happened. I will arrange to get a 120V PT-6 sent to you.

[romanvm]

Got it.

I am getting 120 VAC at the power terminal switch and ect, so you saying it might be a wrong power transformer? Is there a specific test I can do to determan that?

Could you also send a couple of 220 ohms resistors? I had to replace one, it was reading around 370 (A side) and another one is close to 300 ( B side). Should I contact Eileen to get this expedited?


Here is some additional info:

Pics attached show resistance and VDC voltages I'm getting.

Few other things i found:

1. 220 OHM resistor read 350 ohms on A side at A3, I replaced it but with now difference to the readings.. Could that be a problem?

2. In places I should see 0 ohms reading I show 0.1 to 0.3 ohms.. Is that normal?

3. My plate chockes do not have a red/black wire (as described in manual) that supposed to connect to 17L & 19L. It's black..


Thank you all for your help

Roman

[Doc B.]

I have asked Eileen to send you the proper transformer. The 220 ohm resistor value is not critical, and you will never measure exactly 0 ohms on the ground connections. Anything under 1 or 2 ohms is fine there. Not sure what is up with the plate choke wire color. I will investigate when I get to the office.

[romanvm]

Finally got correct power transformer, got it installed and listening as we speak! Wow is all I have to say! 

I am running it with my small studio monitors dynaudio's BM5's, 4 ohms, 86 db sensitivity, DIY silver speaker wire and interconnect wire, source is 24bit, 48hz apple lossless iPod through ALO audio DAC/headphone amp.  I can imagine what it will sound like with great high sensitivity monitors, should I look for something in mid 90 db sensetivity range? Any recommendations?

Do have a quick issue, when trying to set hum balance I can not get it to go below 3.2 mv, I did very fine adjustments.. It says it should be between .8-2 mv. Is there anything I can do to get it down?

All left to do is couple couts clear coat on the base.

What preamps you guys running or would recommend to pair up with stereomour?


Thank you all for your help and my expectations have been exceeded by a mile!!!


Roman

[romanvm]

Also, when I turn volume down pretty low (40 db or so on my spl meter) my right channel volume disappears befor left channel does. I liked to listen to low levels at times, any particular reason for it not being balanced evenly?

Or could it be that my left channel is overall by a few db's louder?

Roman

[Paul Joppa]

The minimum hum is a little dependent on the particular tube. Is it the same on both channels?

I would not consider 2.5mV at all unusual for AC-heated 2A3s; so 3.2mV is not badly out of line IMHO. We must have been lucky when we measured "-.8 to 2.0" for the manual.

Hum also has many possible other sources - was this measured with the volume all the way down and no inputs connected? Is the amp powered from a properly-grounded 3-wire power outlet? Those are tests for possible other sources. Also listen to the sound; a smooth low tone is one thing, anything of a buzzy or sharp nature indicates a different source.

Unbalance at low volumes is a common problem with level controls, at least those that cost no more than the whole Stereomour kit! (OK, I exaggerate a bit there ...) There are various approaches available to adjust that.

If you never need more gain than is available then you don't need a preamp. Some people like them anyhow, of course...