I added diodes between the rect tube in serier with the PT secondary HT leads ?

[catnine]

Before I added them I had 330 VAC on each secondary to the rect tube , after adding them I have 175 VAC and also read DC is this because the diodes rect AC to DC and now I have the diode protestion ? All other voltasge readings have not changed just at the PT secondaries . Is this the way it is supposed to work ? I don't know if I like this mod. I placed the diodes in series.

[Dave H]

I think it's OK. Before you added the diodes your meter calculated the AC voltage from the whole sinewave but now it only has the positive half of the wave so it reads low. It reads DC too because you only have the positive half of the wave so the average voltage is positive.

[catnine]

I don't know . if the purpose of the rect tube is to rect AC into DC then if the diodes in series with the PT HT secondaries and the rect tube convert half the wave and the rect see's both AC and DC voltage then isn't part of the rect tube being defeated?

[R.G.]

The rectifier tube is being *supported*, not defeated.

The real question to ask is whether your B+ voltage is close to the same before and after adding the silicon diodes.

As an aside, measuring the voltage at the point between the solid state rectifier and the tube rectifier is just confusing you. What really matters is the current going through each half of the tube rectifier, not the voltage presented to it. The SS diodes only give the tube rectifiers the half of the AC cycle they would already be rectifying. So they do what they always did, pass the current to the filter caps for that half-cycle.

At a higher techie level, things in series can always be put in any order as long as you do not look at voltages or take currents out of the points in the middle of the series string. The same voltages happen at the end points of the series string and the same currents flow through it to the end points. But the voltages at points in the middle are different with different orders.

[catnine]

The rectifier tube is being *supported*, not defeated.

The real question to ask is whether your B+ voltage is close to the same before and after adding the silicon diodes.

As an aside, measuring the voltage at the point between the solid state rectifier and the tube rectifier is just confusing you. What really matters is the current going through each half of the tube rectifier, not the voltage presented to it. The SS diodes only give the tube rectifiers the half of the AC cycle they would already be rectifying. So they do what they always did, pass the current to the filter caps for that half-cycle.

At a higher techie level, things in series can always be put in any order as long as you do not look at voltages or take currents out of the points in the middle of the series string. The same voltages happen at the end points of the series string and the same currents flow through it to the end points. But the voltages at points in the middle are different with different orders.

I just tacked the diodes to the secondary PT leads since they are 3 amp diodes and the chassis is an old 71 music master bass amp I added a rect tube socket so I need to get the smaller 1 amp diodes since there is so little room .

R.G : I understand now how it works it's like adding three diodes in series as one would on larger powered tube amps and the rect tube is a diode of a different kind . I would have gone SS rect but the PT already puts out a high enough B+ and plate with a 5Y3 and I was not about to add more stuff to cut the voltage down . It's an Allen Amp PT I got in 2005 that is a replacement for a SF champ and all Princetons even with the JJ 6V6's @ 19mA each I have a plate of 414 VDC and I don't want to bias it hotter .

I just didn't build this amp in a large enough chassis to carry the large OT and PT plus a rect tube. This chassis was all I had and made it work. The PT fit perfect in the MM bass amp chassis .

For some reason the 5 volt is at 5.17 VAC and the 6.3 VAC heaters are at 6.47 , I never checked them before on this build . It was only later when I started reading forums and posting that I thought to check more in detail. Raising the bias will do nothing to lower the 5 and 6.3 volt heaters yet they have been like this since 2005 and I have no issues yet, the heater voltage is not that far from spec. The PT I got is capable of running a pair of 6V6's with 5Y3 or a pair of 6L6's with GZ-34 and the mA rating is higher than needed other than the 5 volt for this build.

Even still there are so many other areas for a tube amp to fail there is no way I can add all the protection really required. This build requires a 2 amp line slow blow but I have a 1 amp in there and it's been fine so I left the 1 amp in there.

I am not saying the protection is not a great idea , in this amp it's just not possible and even attempting that would probably create a potential short just by trying to place fuses so close to other components.

[R.G.]

For some reason the 5 volt is at 5.17 VAC and the 6.3 VAC heaters are at 6.47 , I never checked them before on this build . It was only later when I started reading forums and posting that I thought to check more in detail. Raising the bias will do nothing to lower the 5 and 6.3 volt heaters yet they have been like this since 2005 and I have no issues yet, the heater voltage is not that far from spec.

The actual spec on tube heaters is often +/-10%. I'd say those voltages are *remarkably* close to nominal. That should be no trouble at all.

Even still there are so many other areas for a tube amp to fail there is no way I can add all the protection really required...
I am not saying the protection is not a great idea , in this amp it's just not possible and even attempting that would probably create a potential short just by trying to place fuses so close to other components.

That's fine. As per our earlier discussion, tube amps are pretty tough with no special protection in them at all. Putting in stuff without room to do a good job would make the amp less reliable, not more reliable.

Do what you can reasonably do, and feel good that you did that much. Nothing is perfect, and nothing lasts forever.

[catnine]

The actual spec on tube heaters is often +/-10%. I'd say those voltages are *remarkably* close to nominal. That should be no trouble at all.


That's fine. As per our earlier discussion, tube amps are pretty tough with no special protection in them at all. Putting in stuff without room to do a good job would make the amp less reliable, not more reliable.

Do what you can reasonably do, and feel good that you did that much. Nothing is perfect, and nothing lasts forever.

To be honest I would have to move to many leads at the PT just to get even the smaller 1 amp diodes in the space allowed. I just made certain every thing was working as it should be and tied some leads with zip ties to make certain they cannot stand higher than the chassis top and touch the stapled on screen mesh that fender stapled on the inside top of the cab . The only thing I am going to do is get a real 5Y3 since I don't trust the sovtek so called 5Y3 I have in there now . So for it's worked fine and only raises the B+ 10 volts . The biggest pain is that the line voltage in this very old ten unit apt building I live in is the line can very between 118VAC to 119.8VAC so just to check the voltages I need to monitor the line , it's never steady yet the amps voltage over all raises and lowers about the same amount .

[R.G.]

Sounds like a decent plan.

You're lucky with line voltages. I'm on the end of a LOOOOONG transmission line, and the voltage here drops to 110, but can easily go to 128 at times.