Reduction High Voltages

[MisterM]

Finished the Reduction today and all resistances checked OK, LED’s light and all voltages checked within tolerance except those that are to be 70 – 90V (T2,7,13,14,15,18,19,20,26,31). With the supplied tubes, Soviet 6H23n, those voltages are all 115-125V. I swapped them for a pair of EH 6922’s and all voltages are within the 70 – 90V range and it works well and sounds great. Re-installed the 6H23n’s and confirmed the higher voltages. Did I get something wrong? The 6H23n’s are supposed to be better than the standard 6922 according to some tube sites so is it OK to use them with the higher voltage? Will the output be higher? Thanx

[Doc B.]

They may just need to burn in. Run them for 20-40 hours and check the voltage again.

[MisterM]

Left the Reduction powered up for over 50 hrs then measured voltages with my trusty Fluke 85. Line voltage is 122.9V. All terminals that should be 70-90 volts (T2,7,13,14,15,18,19,20,26,31) are 22%-36% over 90V with the 6H23n’s. All other HV terminals (T4,29,50,51,52,53,56,57,59,60) are 3%-6% high but that is within tolerance. All other LV terminals (T33,37,38,39,41,42) are right on.  When I switched to EH 6922’s all voltages are right on the listed voltages. It works and sound fine with either tube so I’ll leave the 6922’s in.  I’m just curious why the voltages are high with the supplied 6H23n’s and will using them cause any harm?

[Paul Birkeland]

For whatever reason, they are just drawing less plate current.  Generally we find that this happens when these tubes haven't been used for a long time, so running them in tends to clear things up and make them work properly.

There isn't any harm in running them at these voltages.

[Paul Joppa]

I agree that in most cases the current will eventually settle at the proper value, though it may take more than 50 hours. I personally consider that a manufacturing failure, but it is so common these days, and so easy to rectify, that I don't worry much. Let it run another 100 hours.

If the voltages are still that high after more time, I would check the 18K resistors (plate loads) for the right value - power off but should be OK without unsoldering them.

Then check the voltage at each end of those resistors.

Report these values here - this will tell us what current is actually flowing. If you have 125v at one plate with 130v at the other end of the resistor, then the current would be 0.28mA, 10 times less than the design value and quite unsatisfactory.

It strikes me as odd that all four triodes (both dual triodes) should all have the same problem.

[MisterM]

Thanks guys for the response. I'll let it cook for a few days and then re-ckeck voltages.

[MisterM]

Left the Reduction powered up for over 200Hrs in addition to the original 50Hrs with the 6H23n’s installed. I assume it was not necessary to have a continuous input signal for tube burn–in but did use the turntable quite often. Voltage results were the same as earlier:

T2 = 112, T4 = 165, T7 = 118 and T26 =116, T29 =164, T31 =122. Also T13 14, 15, 18, 19, 20 are 116. All other voltages are within spec. Trying a pair of EH6922’s or a pair of Sylvania 6DJ8’s gives the voltages as listed in the manual.

For comparison, I also tried these three pair of tubes in my Seduction with similar results (high voltages with the 6h23n’s  correct voltages with the others).

[Paul Joppa]

Bad tubes then.