[Amps] 3CX1500A7 versus 3CPX1500A7

[Robert Morris]

I have step/start and a variac on the filaments. I measured at the pins, with tubes on, then set the panel meter/ homebrew scale to read
5.0. Meter is on the fil secondary, before the fil choke. It's a reference number, set with a Fluke on the pins.

This is a "homebrew Henry" in a 4' rack with lots of panel space for extra knobs and meters.

Power, around here goes off, blips on and off a few times and either stays off or comes back at the voltage of the day... +/- 20.

So I have a small relay wired "around itself" controlling the main relay. If street power goes away, the relay drops and does not come back
until I push the reset button. Don't need 50 uf of caps recharging on blips.

Do the math.... 124*/115 x 5 = 5.39
* or volts of the day...

Look up the Eimac/Broadcast - Bil Orr notes on running filaments a tad low.



On Feb 9, 2014, at 1:19 PM, Larry - WS3Z wrote:

Hi Robert,
Right now it is 5.05 vac BUT my line was '138' when my 8877 tube went.
I did not know it was so high till after the fact, the ups's started beeping and
the tv shut itself off. They brought the line down to 116 (right now). I have been
watching it, it goes a bit lower but not higher yet.

Do you keep a variac and meter on your filaments all the time. I found a circuit from
Bill Orr that rectifies 1 leg with a diode and a zener then a 25K pot on the other leg.

Do you think the high filament could have shorted my tube- cathode to filament ?
Do you monitor the power going into the filament transformer or at the pins.
If so how do you bring the meter lines out of the socket cavity. Everything I put in
goes thru feed-thru caps.

Thanks for sharing you knowledge
Larry
WS3Z



----- Original Message ----- From: "Robert Morris" <robrk at nidhog.net>
To: "Larry Critchfield" <ws3z at lhtot.com>
Cc: <amps at contesting.com>
Sent: Sunday, February 09, 2014 11:36 AM
Subject: Re: [Amps] 3CX1500A7 versus 3CPX1500A7


Do you know what the voltage at the pins measure now?

Unless you have a variac in line, I bet it's not 5.000.

Most of the old transformers in my junk box are 115v.

My line voltage, as we speak is 121 and has been know to go to 124.

Calls to the power company, in summer, when they are fighting all the air conditioning and it goes to 127 and all my UPS's start yelling.

A 100 watt Variac or Powerstat and a meter calibrated at the pins, fixes both issues.

.


On Feb 7, 2014, at 12:13 PM, Larry Critchfield wrote:

Hi John,
Do I have to worry about the .5 volt filament voltage for the 3CPX ??
I do not want to modify my amp for 5.5 and then have to switch back
to use my 8877's plus the cost of new parts.
Thanks
Larry
WS3Z
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