Finished GSG - Help needed!

2nd harmonics for the masses

Finished GSG - Help needed!

Postby whaam68 » Sun Oct 05, 2008 11:45 am

Image

Image

Finally got this finished, it's my 2nd amp. The transformers are Dynakit (power) & Transcendar Outputs. All the tubes are Soviet ebay. I had a couple of FT3 teflon coupling caps & wanted to try them but it was a squeeze "under the hood" but I've used Russian Teflons in an old heathkit before & they sounded very nice. I hooked it up & it powers up fine & didn't blow up! but there is only very feint audio coming out of the speakers so when I get the time in the week I will test the voltages & report back for advice if I can't get it (took me a week with amp 1 to figure out I'd shorted the inputs to the chassis! so I guess I will start there.
PS what's the best way to tighten up the grip on a valve socket..one of the 6B4G's feels a bit wobbly.
PPS I'm using a choke...should I have left out a resistor?
Mike
Last edited by whaam68 on Fri Oct 10, 2008 12:12 am, edited 1 time in total.
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Voltage checks done...let the "fun" begin!

Postby whaam68 » Thu Oct 09, 2008 2:03 pm

OK

finally got time to run some checks using the chart in the manual: Load on the speaker, no input

V1 6SL7
Pin
1 ok
2 142v not 147
3 ok
4 ok
5 142v not 147
6 ok
7 3.3v A/C NOT 6.3v A/C
8 3.3v A/C NOT 6.3v A/C

V2 6AX5GT
pin
1 ok
2 3.8v A/C not 6.3V A/C
3 346v A/C not 324v A/C
4 ok
5 346v A/C not 324v A/C
6 ok
7 3.38v A/C not 6.3v A/C
8 ok

V3/V4 6B4G
Pin
1 ok
2 44v not 54v
3 ok (305v not 308v)
4 ok
5 ok
6 ok
7 ok? (50/51v not 48v)
8 ok

J1/J2
pin
1 ok
2 ok

J3/J4
1&2 3.3v/3.3v NOT 6.3v
3 0.8v/0.8v not 0v
4 50.6v/50.9v not 54v
5 44v/44v not 48v

J5
pin
1 337v not 333v
2 330v not 327v

J6
pin
1 347v not 324v
2 ok
3 ok
4 347v not 324v

J7
pin
1 ok (321v not 319v)
2 ok (321v not 319)

This amp uses a dynakit power tx for 240v (although when I got it it was marked 230v) clearly the heater voltage is about 1/2 what it should be & the power tx 2ndry is putting in more voltage than specified.

Any ideas on where to start would be appreciated! You can see my metalwork is better than my electronics knowledge!
Mike
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Postby whaam68 » Sun Oct 12, 2008 1:22 am

OK I've figured I should have been measuring the heater voltage from pin to pin & when I do the heaters are OK. I'm getting audio from both speakers but very low & only when the vol pot is cranked right over...anyone got any ideas? I have re touched all the joints on the board but still no joy Yellow_Light_Colorz_PDT_13
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Postby TerrySmith » Sun Oct 12, 2008 7:11 am

I would disconnect wiring at the inputs and run wires directly from the input jacks to the circuit board, then check operation.

Are those coupling caps good? Make sure the cans are not grounded. Maybe try unhooking them from the board and trying different caps.

Your voltages look good.
T. Smith
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Postby whaam68 » Sun Oct 12, 2008 1:08 pm

Hi Terry
I have just whipped out the big FT caps & offboard wiring & wired in a couple of K40 Russian PIO's that fit on the board....no difference
The FT's were mounted on plastic spacers & although tight there is clearance on the can to chassis & other bits. Now I know it's not the caps I will re wire the inputs direct to the board bypassing the pot & see what that does. I'm thinking the input RCA's might be grounding to the steel chassis although I took care to see there was clearance...I might take off & file out the holes for the inputs & speaker connectors.
Probably tomorrow! Yellow_Light_Colorz_PDT_09
regards
Mike
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Postby whaam68 » Mon Oct 13, 2008 6:35 am

I bypassed the Pot & now the amp is working fine...well better than fine
The quality of this little amp just blows me away. Not sure what the prob with the pot is but I may just leave it bypassed for now as my preamp has a vol pot on it.

I'm using the GSG to drive some mid 60's 3 way 15ohm wharfedale's with 15" woofers & the Bass & detail are just amazing. I'm really impressed with the GSG. It seems louder & warmer than my Tubelab Simple SE which has massive 11lb 5K Edcor outputs, not sure if I built it badly or my speakers prefer the 3k Transcendars. I was planning to use this with some old full range drivers in te bedroom but it sounds so nice I will put it in the main system.

For 240v builders I'm using a Power Tx from dynakit which seems to work fine..runs a little warm but not too bad & doesn't break the bank.

Thanks Shannon! Great design
Mike
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Postby EWBrown » Mon Oct 13, 2008 4:49 pm

I like those Russian K40y coupling caps, they come very close to the legendary Sprague "Vitamin Q" PIO caps, at a tiny fraction of the "Q" prices.

Those vintage 15 ohm Wharfedale systems were pretty nice sounding speakers, as I remember them from the later 1960s. I just recently traded away a "collection" of 40 year old, unused 8, 12 and 15 inch, 15 ohm (actually marked as 10 to 15 ohms) Wharfedale drivers. Too much "bulk" and weight for the in-process move to NC...

/ed B
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Postby whaam68 » Tue Oct 14, 2008 6:27 am

The K40's definately sound nice in my GSG, I have used K42's & teflons in an old heathkit & that also sounded great. I don't think old soviet tubes & caps can be beaten for performance vs price. The Transcendar outputs also seem to be excellent performers. Bit of a shame to sell the Wharfedale's...all my speakers are vintage, & I'll keep em as all my output tx are 15ohm
Mike
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