2. amps-preamps
  3. 140298-93362

Joule-Electra VZN OTL Users- I Need advice!

Got my VZN 100’s about a week ago and there are things Id like to get advice about.

Variac:

1. When firing up, do you set it a bit lower than the destination voltage of 65v and after warm up adjust to final destination voltage?

2. Voltage reading is different each time when the dial reaches a point that i marked on the Variac dial. Is that normal?
I would mark the point on the dial, say 65v, after the amp worked for a few hours, but the next day the same point on the dial will give me a different voltage reading.

3. I get +- 3 volts of fluctuation throughout the day. Is that normal? Sometimes i get both blocks to read almost the same, then 30 minutes later one went down 2 volts and the other went up about 2 volts.

4. When aiming for 65v, should the higher of the pair be at 65v or should i get an average of 65v (i.e L-67v/R-63v for example)?

5. For some reason the Bias is not necessarily corresponding to the voltage reading.
In other words, say i biased the tubes to be at 28 when the amp voltage is at 65.
The next day, or after few hours, the same 65v reading gets a different bias reading, as if the tubes fluctuate even in reference to the same voltage within hours- not days/weeks/months.
Its as if i have to rebias all the time. It don’t make sense...

Power cycles:

1. Is it safer/better to shut the Variac off if im not listening for aprox 4-5 hours?

2. Is it Safe/Better to lower the voltage, but not shut off when i go out for an hour or not listening for an hour to a few hours?
It seems like it might make more sense to lower the voltage with the Variac than completely shout off, but i am wondering if it might damage the amp to sit idle at lower voltage than it expects (without playing music).

Tube rolling:

Whats your experience in rolling for the driver and input tubes? Not talking about the output tubes.

Thats my questions for now. Please feel free to add whatever your experience with these unique beasts taught you.

Thanks
Rea
dumbeat

Showing 3 responses by atmasphere

atmasphere's avatar
atmasphere
12,088 posts
 
He continues to offer that service, and with all due respect to Ralph, probably knows a much about the products as anyone currently active.
FWIW Rich and I work together to support the legacy JA products.

When you are going to leave for more than a few minutes shut these amps off ! Respect the 6c33 and their power ! Yes it's a pain but the quality of the sound, as you've alluded to, is well worth the hassle.

This is really good advice. FWIW, the 6C33 has a way of slowly eating its socket so I would keep it off if unattended. 
atmasphere's avatar
atmasphere
12,088 posts
 
Do you recommend to keep voltage at 65 and slightly bias low (say 26?)

As far as keeping the amp in standby, aren't the little tubes more sensitive to powering cycle than to staying on at minimum power "standby"?
Yes to the first- try it and see- reducing the bias may affect the sound.
To the latter, in a word, no. The power tubes are why this amp uses a variac. I don't like the system- requires too much fiddling from the user- but its the power tubes that can be damaged if the B+ is applied prematurely before they are warmed up. 6C33s need about 5 minutes for that, FWIW.  
atmasphere's avatar
atmasphere
12,088 posts
 
Your experience is one we've heard about fairly often.

If you're not planning to use the amp for a few hours, you can totally turn it off. No need to run at a reduced voltage- that will slowly eat the tubes. But it is a good idea to do the slow start.

There are motorized variacs that can maintain output voltage as the AC line fluctuates.

Its also pretty normal and a bit unsettling to see the bias variations, but the amp is known for that. I've been told a number of times by customers that you have to keep an eye on it.
The 6C33 power tube has a very high transconductance number and it is affected by heat- it can get into a sort of thermal runaway if it gets hot enough. I'd be conservative about the bias if I were you!
More to discover