Considerations when replacing GZ34 with 1N4007's

[nevetslab]

Ah how true this was.

SO back in the shop today, confirmed what I knew; the pins did not even REACH the little "grabbers" on the pin socket bottom, so tightening them would yield no results!

WHAT I DID NOT KNOW was that the eyelets holding the grabbers had become a little loose over time, letting the "grabbers" travel about a MM or two lower than they should, and the "grabbers" themselves were bent upwards slightly. So, carefully flattening the edges of the eyelet, the "grabbers" dropped back down a smidge, close but not perfect. Then I VERY carefully bent the "grabbers" down a little bit and re-tensioned them as I normally would any socket.

This was as humiliating as it was effective.

Looking back at last week, my landlord sold the property so I've been filling out housing applications all week, one of my best friends was moving to New York, my partner started a new job, our band coordinated our first show in 2 years, and our shop was finally returning to full 40 hours for amp work so I was already a bit stressed out and definitely absent minded... thank you guys for getting me "up in that front seat".

Here's a pic of the socket (after doing the eyelet press / re-tension):

I've never seen one of these sockets before. Now, seeing brass rivets on this side of the ceramic base, I'd have to believe there would be substantial space between the opposite side and an additional insulator....or just plenty of space so there's sufficient spacing between Ground (chassis) and any of the pins at their elevated AC voltage/DC voltage. So, does it seem longer pins are needed on any rectifier tube inserted, due to that space requirement between live rivet heads and the chassis surface we're seeing in this photo? It looks like a good quality socket. I'm guessing a Russian connector?

Using a wooden Q-tip shaft or something similar, see what the length is needed from the top surface of the connector to passing thru/past the contacts. How much longer is it than the typical octal pins on any of the octal tubes you have.

How thick is that ceramic base? Can you get any photos showing more of the thickness/height of that ceramic base? Very interesting connector

[Enzo]

Would love a photo of the empty socket from the top side.

[glebert]

Would love a photo of the empty socket from the top side.

Wondering if it is one of these. https://tubeworldexpress.com/product...rt-122-228-200

[nevetslab]

That looks like what's installed to me. The point of pin engagement by the terminals does look a touch further than traditional sockets, but not such that there would be no mating as in this case. Now, if there's any additional spacers placed between the socket's built-in spacer and the chassis, then it would set it further down....but, assuming the tube base mates with this ceramic base, I don't see why there would be the problem described..

[Mick Bailey]

The socket fitted looks like the Chinese ones I referred to in #18. The type was originally used with transmitting tubes but as usual they get cheapened. For some reason the UX5 types I use for 807 tubes have always been fine, but I gave up early on with the Octal bases because even when new there wasn't much engagement. The rivets can be expanded slightly if loose and the flared end soldered to the contact. I quite like the backing spring that maintains the contact pressure and I guess in the original versions they worked fine and there were no problems.

[Mr_bibbles]

I'll try and get more pictures soon! The amp is one of two that came in together so should be here for a while. After I re-tensioned the sockets and the eyelets the socket works quite well and even "Snaps" into place with the pins, locking it in without a retainer.

[Mr_bibbles]

Sorry about the delay here's a bunch of pictures!

[Enzo]

And I am guessing the base of the tube doesn't fit through the chassis hole? SO you can never push th tube pins all the way in. The tube in the manual photo looks like it might have been a button base type, which ought to fit.

[nevetslab]

Could you please do us all a favor and install the 5AR4 Rectifier tube into this socket, so we can see if it DOES pass thru the chassis opening. If not, and is unable to pass thru to seat onto the tube socket, THEN we will finally understand what it's taken 37 threads to learn.

[Mick Bailey]

This was covered in post #7

Enzo, the tube base fits flush with the socket base and not the chassis itself; it mates with the socket perfectly. THEN, while it's kissing the plastic, you can see the pins travel underneath and just barely even reach the actual socket pins. It's astounding.

[nevetslab]

OK, so back to interpreting all we have to work with. The ceramic base is 5mm thick. Tube pin length is typically 10mm, so IF the tube is sitting flush on the ceramic base, passing thru the chassis opening, then you have 5mm of pin length left to engage the mechanics of the nice spring-loaded socket terminals. And, you're telling us that isn't long enough to pass thru and fully engage the terminal contacts. While the photos above seem to show there is sufficient space to engage them, there must be some mechanical reason why they're not. The ceramic base is recessed 10mm plus the metal thickness of the chassis (1.5mm). Typical tube base diameter is 33mm, it looks like the 5AR4 I have in my hands would pass thru that opening, and have 5mm to fully engage the contact springs. If they don't, then the mfgr of the tube sockets has no business selling those for that purpose. So, what are we missing here?

[Mr_bibbles]

Guys! The issue has been resolved, I detailed in the post above (although I didn't word it as clearly as I should have! I ended up carefully re-flattening the eyelets and then re-tensioning the socket and it worked. I think I was thrown off by the goofy design and the fact that the socket pins wouldn't even reach the tube before the eyelets were straightened out.

These pictures were more for the curious. Thanks again for all the help!

[Mr_bibbles]

One curious question though, are any of you experts able to deduce what's going on with that goofy hum adjuster? I have never seen anything like it before.

[Helmholtz]

One curious question though, are any of you experts able to deduce what's going on with that goofy hum adjuster? I have never seen anything like it before.

Well, it's a simple humdinger (hum balance pot), which uses the cathode voltage for heater elevation.
300B is a direct heated triode, where heater/filament = cathode.

[Mr_bibbles]

Well, it's a simple humdinger (hum balance pot), which uses the cathode voltage for heater elevation.
300B is a direct heated triode, where heater/filament = cathode.

Ah, so as you were asking earlier, why would this affect the DC offset at the speaker? It seems like using an ear would be the easier method and effective to boot...