How much damage can I do?

[sonicmojo]

Running 5V heater rated power tubes in a 6V heater circuit? I know I SHOULD PROBABLY NOT DO THIS but I have some 5CZ5 tubes that I want to run in place of some 6CZ5 tubes just to see how they sound in a Supro 1622RT (newer issue amp). As far as I can tell, these tubes are the same but different heater specs. 6CZ5 tubes run fine in this amp (6973s are stock) as the connections in the circuit allow for this. I am curious as to how a 1V increase in heater voltage will affect and/or damage the tube or the amp. I really don't care about the tubes, but don't want to destroy the amp. I've tried to search and Google and such but cannot find any real info to go by. And yes, I am known to be a bit of a hacker and experiment....

[martin manning]

Running with a 20% overage they would probably not last long. Can you put a reversed pair of 1N4007's in each leg of the 6.3VAC feeding just those tubes? That would be just about perfect.

[sonicmojo]

Running with a 20% overage they would probably not last long. Can you put a reversed pair of 1N4007's in each leg of the 6.3VAC feeding just those tubes?

Hi Martin. Thanks for the feedback. I know it is a bad idea. I put them in for a minute and they work but got hot pretty fast. It is probably difficult to inject any mods into this PCB design so I'll stick to the tubes that are more likely not to explode!

This amp came used to me with old Sylvania 6CZ5 tubes but it came stock in 2018 with EHX 6873s. It works fine with the 6CZ5 tubes.The only difference between 6973 and 6CZ5s that I can see is that Pin 8 to Grid2 on 6CZ5s is not connected. This does not seem to be a problem because the signal must come in on Pin1 (to Grid 2) with this particular amp design. My question is, would there be any benefit in jumping Pin1 to Pin8? If you look at the tube pin outs, it appears that the opposing pins (1/8) go to different sides of the grid on the diagram for the 6973. Would it make any difference if I were to jumper Pin 1 to Pin 8 on the PCB to make up for the internal tube difference? Or is this irrelevant?

https://www.bustedgear.com/images/jobs/ ... Z5-9HN.jpg

https://www.bustedgear.com/images/jobs/ ... 73-9EU.jpg

[martin manning]

The data sheet for 6CZ5 says IC (internal connection) for pin 8. Maybe you can make some measurements to see if pin 8 goes to any other pins, but I usually take IC to mean "don't use this pin."

[sonicmojo]

Also, if you look at the diagram for 6CZ5, grid 1 pins 3 & 6 are connected on the same side of the grid, but not on the 6973. I don't know if pin connections on same or different sides of a grid or any other component inside a tube make a difference or not. That is part of my question and any insight would be awesome. Thanks!

[sonicmojo]

The data sheet for 6CZ5 says IC (internal connection) for pin 8. Maybe you can make some measurements to see if pin 8 goes to any other pins, but I usually take IC to mean "don't use this pin."

Pin 8 on the 6CZ5 and 5CZ5 does not seem to have any connectivity to any other pins but 3 and 6 measure low resistance.

[sonicmojo]

I don't yet have a 6973 to measure pins 3 and 6 but I have ordered a new set to see if it has any effect. At least with them I'll get the amp back to stock specs. Thanks!

[sluckey]

Look in the For Sale/Trade section for a good deal on a matched pair of 6973s.