Rectifier modification for the GZ34

Hi all:
I found these two versions of this rectifier mod for ST70's ising a GZ34 or equivalents on DIY threads and thought it would be of interest to those who have been having problems with tube rectifiers. Looks pretty simple and and easy. Both appear to be the same mod.
baddog1946

http://www.diytube.com/phpBB2/viewtopic.php?p=31759&sid=6cebd09b7841b53734767346943d0123



Van Alstine version:
For your information, we recently posted a small upgrade to our Ultimate 70, Ultravalve, and even stock Dyna St-70 amplifiers. All that is necessary is to install two 1N4007 diodes, one in series with each high voltage power transformer lead to the 5AR4 rectifier tube. The diodes will mount on unused 5AR4 socket pins. The purpose is to prolong the life of the rectifier by reducing the impact of cold hard turn-on AC voltage to the tube.We recommend this for any vacuum tube amp using a 5AR4 rectifier tube.[u]

I put this Mod in last night on my ST-120. This is real easy to do. I had the copper braid to clean up the De-solder the wires from 4 and 6. The two 1N4007 Diodes were under a buck.

I put some $$ into a GZ34 so I thought it would be worth the time to do this mod. Put it in and back to sweet music.

Here is a plan I got from the friendly people at Dynakit.

After I did this mod the voltage readings on pins 4 and 6 decreased quite a bit...to about 203VAC. Pins 5 and 7, the pins with the PT leads, still test normal at about 379.5VAC (albeit a little high.)

I assume this is normal?

Ed

After the diodes on pins 4 and 6 you have to set your meter to DC. You will measure pulsating DC before the filter capacitor, set your meter to DC and measure at pin 8 of the 5AR4 tube.

Sal

Call me crazy, but I think the PT's in both of my 70's are running a tad cooler after this mod?

xlr8 wrote:Call me crazy, but I think the PT's in both of my 70's are running a tad cooler after this mod?

Can anyone else confirm this? Does this mod take some load off the PT? You're still powering the rectifier filament...