Isolation Transformer an Option?

Repeated the exercise sans cheaters. Same result, all low mV, and no potential between two chassis. Individually on their own both amps are silent. Could the new power tubes I recently installed be helping? (re-tensioned the sockets at same time)

LeGrace wrote:Repeated the exercise sans cheaters. Same result, all low mV, and no potential between two chassis. Individually on their own both amps are silent. Could the new power tubes I recently installed be helping? (re-tensioned the sockets at same time)

Could be on the power tubes.

Could also be that your shock was as simple as touching the live end of the fuse holder. For your sake, I hope it is as simple as that. Just please be sure that there is nothing visibly untoward going on - now that you have provided a level of reassurance to those here of your safety.

Thank you for doing this!

Peter W. wrote:

LeGrace wrote:Repeated the exercise sans cheaters. Same result, all low mV, and no potential between two chassis. Individually on their own both amps are silent. Could the new power tubes I recently installed be helping? (re-tensioned the sockets at same time)

Could be on the power tubes.

Could also be that your shock was as simple as touching the live end of the fuse holder. For your sake, I hope it is as simple as that. Just please be sure that there is nothing visibly untoward going on - now that you have provided a level of reassurance to those here of your safety.

Thank you for doing this!

I was touching it. Normally I position the fuse in the holder cover first, but not that time.

LeGrace wrote:

Peter W. wrote:

LeGrace wrote:Repeated the exercise sans cheaters. Same result, all low mV, and no potential between two chassis. Individually on their own both amps are silent. Could the new power tubes I recently installed be helping? (re-tensioned the sockets at same time)

Could be on the power tubes.

Could also be that your shock was as simple as touching the live end of the fuse holder. For your sake, I hope it is as simple as that. Just please be sure that there is nothing visibly untoward going on - now that you have provided a level of reassurance to those here of your safety.

Thank you for doing this!

I was touching it. Normally I position the fuse in the holder cover first, but not that time.  

It's useful to have a master switch (could be as simple as manually tripping your GFCI -- or toggling the on/off switch on a Furman-type power regulator) before handling "live" AC. This won't protect you from charged-up caps but it does result in fewer hazardous conditions.
Not to be a kill-joy, but you may still have an intermittent problem and just got lucky when you performed the voltage potential tests that PeterW wisely recommended.

What encourages me most is a big change in the bias stability on the problem amp. I maintain a daily log in a notebook. I'm observing around a 10 fold improvement, starting the day I replaced the power tubes. I now monitor line voltage daily as well, seeing spikes up to 121.5v. Maybe what I really need is a variac, versus isolation transformer?

LeGrace wrote:What encourages me most is a big change in the bias stability on the problem amp. I maintain a daily log in a notebook. I'm observing around a 10 fold improvement, starting the day I replaced the power tubes. I now monitor line voltage daily as well, seeing spikes up to 121.5v. Maybe what I really need is a variac, versus isolation transformer?

OK - and cutting to the chase:

Let's look at the (relative) cost of your electronics.
Let's look at their care and feeding (tubes).
Let's look at the replacement cost if damaged.

Writing for myself, I have about $8,000 in replacement costs tied up in my front-line system focusing only on those items that are in any way unusual or hard to find. Note that this is around half the cost of a present-day replacement in equivalent quality from a similar (or the same) source. I insert this as my newest front-line item is c. 1984 being my Maggie speakers. Their present-day equivalents are ~$13,000 a pair. And so on.

So, an active true-sine-wave line conditioner would seem to be a wise investment under the circumstances. And about the only set-and-forget option. NOTE: It is NOT a UPS. It is a Line Conditioner.

https://www.tripplite.com/shared/product-pages/en/LCR2400.pdf

This one comes to mind as not terribly costly, and well-reviewed. Writing only for myself, it does the trick for both solid-state and tube equipment.

Peter W. wrote:

LeGrace wrote:What encourages me most is a big change in the bias stability on the problem amp. I maintain a daily log in a notebook. I'm observing around a 10 fold improvement, starting the day I replaced the power tubes. I now monitor line voltage daily as well, seeing spikes up to 121.5v. Maybe what I really need is a variac, versus isolation transformer?

OK - and cutting to the chase:

Let's look at the (relative) cost of your electronics.
Let's look at their care and feeding (tubes).
Let's look at the replacement cost if damaged.

Writing for myself, I have about $8,000 in replacement costs tied up in my front-line system focusing only on those items that are in any way unusual or hard to find. Note that this is around half the cost of a present-day replacement in equivalent quality from a similar (or the same) source. I insert this as my newest front-line item is c. 1984 being my Maggie speakers. Their present-day equivalents are ~$13,000 a pair. And so on.

So, an active true-sine-wave line conditioner would seem to be a wise investment under the circumstances. And about the only set-and-forget option. NOTE: It is NOT a UPS. It is a Line Conditioner.

https://www.tripplite.com/shared/product-pages/en/LCR2400.pdf  

This one comes to mind as not terribly costly, and well-reviewed. Writing only for myself, it does the trick for both solid-state and tube equipment.

Peter, the price is right compared to the $2k Furman I have. Question I couldn't find an answer to is does it output a pure sine-wave like a Furman? Says "computer-grade" but that could be a square wave. The voltage ranges are about right, for sure. Not sure there's room in that box for an autoformer.

Peter, the price is right compared to the $2k Furman I have. Question I couldn't find an answer to is does it output a pure sine-wave like a Furman? Says "computer-grade" but that could be a square wave. The voltage ranges are about right, for sure. Not sure there's room in that box for an autoformer.[/quote]

I take a primitive approach to these things - does it work? Yes.

On a scope (yes, I have one - barely used)  it gives what looks like a pretty clean sine-wave. Certainly no discernible noise. Keep in mind that as it is NOT an inverter system as would be for a UPS, the complexities involved are less than for an inverter-based system. I have seen smaller utility-grade inverters (AKA "Grid-Tie Inverters") for solar systems, so I know that the technology is right there.