Heater voltage tolerance

[xsubs]

I've just bought a VHR cap kit for my '78 DR105 (still has the originals which are starting to "bulge"), and while servicing the amp performed some measurements. My heater voltage is running a bit high... ~3.5VAC to gnd on each side. That puts the voltage at 7VAC, which is around 10% higher than spec. Considering that wall voltage is usually ~124VAC in my locale, that sounds about right. Is there an issue with running this hot?
I have been looking at the Weber "Browner" to lower the input voltage, just a bit, to 115VAC. That should bring everything more in line with the specifications the amp was built around. Does anyone have any input on the Weber unit, or experience with any similar devices?

Thanks!
Cheers
Sean

[OldSchoolDave]

Does anyone have any input on the Weber unit, or experience with any similar devices?

No experience with the Weber solution, but I bought a Belkin PureAV PF60 after seeing Bill Jansen use one at VHC II. I now use that for my home theater stuff. In reviewing the on-line specs, it appears as though it's more geared towards filtering than power regulation (I'll check the manual to be sure). They do make a battery backup unit in the same series that claims to offer Automatic Voltage Regulation:

http://catalog.belkin.com/IWCatProductP ... _Id=195291

Ignore the list price. There are lots of folks selling new units at significant discounts on the 'bay.

Dave

[Chris9723]

Hey there! I wouldnt be too worried about 124. Amperage is always the key IMHO.
The draw on a 12ax7 is around 300mA,I think thats the most key part of the voltage.
If the PT was shooting lots of amperage, you may have a problem, but should be ok.
Max heater cathode voltage on a 12ax7 is around 180v,and max on the plate is around 300v.
Max neg DC grid voltage is 50v ish and positive DC grid is 0v....max plate dissipation is 1 watt.
You'll never overpower one in a preamp circuit,im quite confident,
If any of that makes sense.....I may have confused myself!!
One of the big hitters may want to chime in...but I think your okay.

Voltage regulators for the most part are power filters as opposed to actual voltage regulators. Many work the same as filter caps to prevent hum and voltage spikes, providing cleaner power of the same original voltage.
CHeers!
C

[mhuss]

10% high (or low) on the heaters is OK. I use a Vintage Voltage Adapter to knock down the US mains at my house to 117 or so.
http://www.instructables.com/id/VIntage ... Equipment/

--mark

[xsubs]

10% high (or low) on the heaters is OK. I use a Vintage Voltage Adapter to knock down the US mains at my house to 117 or so.
http://www.instructables.com/id/VIntage ... Equipment/

--mark

Thanks for the info Mark... looks perfect. I like the idea of getting a step-down transformer and line isolation at the same time. Did you use the xfmr in the link you provided, or something else?
I looked around and thought this might be more suitable:
Hammond 166P10
http://www.hammondmfg.com/166.htm
It's a 10VCT@5A model, which should work well as my supply voltage is fairly constant @ 124VAC
Cheers
Sean

[mhuss]

I bought that transformer because it was cheap! The Hammond would work as well.

Note that the VVA does *not* buy you line isolation, just knocks down the voltage on the 'hot' wire a bit.

--mark

[xsubs]

Yeah I just noticed that after seeing the connections on the transformer... since you're bring line voltage over the the secondary side too.
As always THANKS Mark!

Cheers

BTW - my VHR cap kit just arrived... FAST shipping (Thanks Clayton!) and great quality. I'll be busy this weekend