Reduction Finished - Voltage?

[Chris65]

Just finally finished my Reduction build, all went well, thanks for the great kit.
Doing the resistance checks, all good then installed supplied tubes & moved onto voltage checks. All good except one side several terminals connected together (7, 13, 14, 15) were nearly half expected at 45VDC.

Mmm, touch up some joints, no change. Ok, thinking - swap tubes. Yep, that's it, low voltage swaps sides. So, I pop in another pair of tubes & yes, all good, voltages match both sides at 75VDC. Bad tube then.

So, what is an acceptable minimum voltage, the specified 70V or close?
Also, measuring one terminal each side (14 & 19 I think it was), the LED centre pin to pin 3 would flicker briefly, is that expected?

Played a few Lp's and does sound good already and dead quiet. Thanks again.

[Grainger49]

Chris,

If you are measuring voltages, with the Reduction on, and the LED flickers there must be a weak solder joint. 

If you are measuring resistance and the LED flickers it is responding to the voltage across it.  Sounds OK to me.

Of course if it sounds good, sit back and enjoy the fruits of your work.  If the LED solder is weak it will show up later.  Most like the channel will go dead and you will know exactly where to look.

[Chris65]

Hi Grainger,

It was the voltage check with the LED lit, just a momentary 'flicker', just dims slightly very briefly when the probe initially touches the terminal. Did a 'chopstick' test & seemed good.
Yep, it sounds good & I will enjoy, thanks.

[Grainger49]

Spin some vinyl and sip an adult beverage.  On a holiday it is allowed all day long.  It is required in the South if you are Barbequing a pig.

[Chris65]

Just a bump for my original question (in the first post) - is a supplied tube that measures at 45VDc (should be 70VDc) acceptable.
What would be a minimum voltage?

[Paul Birkeland]

45V would be considered a high emission tube.  You could also measure the 18K resistor to be sure it's in good spec. 

A bad tube is going to measure more like 95V on the plate.

[Chris65]

Ok, thanks Paul. it's not bad then. Which particular 18k resistor?
All other readings (resistances & voltages) are within spec.

Other tubes (Sylvania 7308, Telefunken E88CC) give good readings (around the 70V range) both sides & are more less equal (within 2 volts).
The supplied tubes, one is 45V other is 72V (swapped either side) - Does that represent a channel imbalance or is what we're measuring not directly related to tube/audio performance?

[Paul Birkeland]

It could represent a channel imbalance, but the question is whether it's anywhere near audible when you convert that imbalance into dB.