• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tubelab SPP first timer build

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#363
jcalvarez said:
Before that I always check for short circuits, both heater and B+ circuits. After that I always do a power up without tubes (electrolytic caps must handle the full peak B+), and measure heater voltage on tube pins, B+ rail, plates etc. At no load everything should be close to B+ peak.
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Good to see you think alike, ill do that tomorrow and see, i'll write down measurements as i go along
 
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#365
#367
Hoorah!
First checks done.
No valves inserted as a precaution.

Mains supply is this morning as high as 246 and not 240!
Checked 6.3VAC, it was at 6.8, bad news....
Checked 5VAC, it was at 5.6, again bad news.
Checked the 300-0-300 and as can be expected it was too high, actually being close to 325-0-325.

I'll now rewire the mains transformer not to 240VAC but use the tap +10 being 250VAC
 
#370
For reference, here are the unloaded values for a 372JX Hammond. You can see the 6.3V winding at 6.78V.

1672915103553.png
 
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#372
Ok, i've now got the Mains Tx wired to 250VAC.
And with the light bulb wired in series with the live (brown) cable i have these voltages.
T1-RED-1 }
T1-RED-3 } 490VAC

T1-GRN-1}
T1-GRN-2} 5.1VAC

T1-YEL-1}
T1-YEL-2} 4.2VAC

Might now insert the valve rectifier Sovtek 5AR4 and check what D.C. output i get.

Depending how things continue, i might revert back to 240 and check voltages again, agreeing with JCAlvarez there is no load.
 
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#373
It is a leap of faith!

Remember this is a proven design, built in the hundreds. The issues you are being cautious about are construction issues, most likely the wiring of the peripherals. Those are best tested by reverse engineering what you have constructed and comparing with what you intended.

It is nice to build the same way as a lighthouse. Once on land, then dismantle and build again in the sea.
 
#374
Thanks Old Hector. Yes it has been build in their hundreds, based as we know by the great design by George of Tubelabs.
Due to purchase costs, import duties, and lots of stress i am being extremely cautious and i will not rush the build.
Yes, this build has taken me far too long, but with limited free time this is what i am faced with.
I do appreciate all the guidance by all the posters, so thanks again all.
 
#375
I've managed to quickly changed back to the 240V tap.
The bulb is still connected, so considering results, i'll now remove the bulb.
With the ECC81's and EL84 inserted i have: -
T1-GRN-1}
T1-GRN-2} 6VAC

Without the valve rectifier Sovtek 5AR4 i have: -
T1-YEL-1}
T1-YEL-2} 5.2VAC

And the 600VAC I have: -
T1-RED-1 }
T1-RED-3 } 602V

Things are looking good
 
#376
Just checked voltages again, without the in series light bulb.

ECC81's and EL84's inserted i have: -
T1-GRN-1}
T1-GRN-2} 6.4 VAC

Without the valve rectifier Sovtek 5AR4 i have: -
T1-YEL-1}
T1-YEL-2} 5.5 VAC

And at: -
T1-RED-1 }
T1-RED-3 } 640 VAC

I think i need to reduce the 6.4 VAC down to a safe 6.3 VAC, i don't want to over work them.
 
#378
If you look at the data sheet I sent you will see the limits for the heater voltage are 5.7...7V. You are very safe with 6.4V.

I'm more interested on the B+ when you plug the rectifier tube. 640 CT unloaded may result in B+ a bit high when loaded, depending on the power transformer wattage.
 
#379
Weekend gone, so back to the drawing board, with care...
I have my 100 watt bulb connected and can report these voltages: -
6.3V = 3.7 VAC
5V = 3.2VAC
B+ = 203 D.C.
Remove bulb and get out the fire extinguisher? 🙂🙂

Or maybe a kick up the rear and get on with it!.............. don't answer that....
 
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