Tubes Asylum

Posted by David McGown (A) on July 30, 2022 at 08:48:39

I borrowed a quad of Psvane EL34PH tubes from a friend (he offered!), and both he and I observed that they are very tight in the socket and cannot be fully inserted into the sockets. So did not force all the way into the sockets, but just made sure that the tubes were inserted enough so the socket would tightly grip on all pins. Just a point of reference, both my friend's amp and mine use Belton sockets. First, the tubes sound absolutely wonderful, so no complaint there, it is wonderful to have current production tubes that equal NOS sound. However, I had a problem in taking one of these tubes out, even as I was gripping the base and not the envelope, perhaps accidently exerting a little side force against the top of the envelope, which caused the cement to fail and envelope loosen and lift slightly from the base. Anyway, inspecting the tube afterwards, the envelope and wires completely seperated from the base, i.e., apparently a poor solder job to the tube pins.

Now, I wanted to determine why these tubes are so difficult to insert and extract, since this is probably what resulted in the conditions of the failure. I got out my digital calipers and measured pin diameter and keyed post diameter and compared it to the dimensions on a Psvane EL34-C tube (other nice sounding tube, BTW). Both the EL34PH and EL34-C had the same pin diameter (2.35mm) and keyed post diameter (checked but not recorded). Proceeding to measure the pin circle diameter, the EL34PH had a diameter to the outside of the pins of 20.35mm (which results in a pin circle diameter of 18mm). The EL34-C measured at 19.9mm to the outside of the pins (the pin circle diameter is 17.55 mm). According to IEC 60067, the specification for the pin circle diameter for a octal socket/base is 17.45 mm. So apparently the special teflon and metal base that Psvane uses does not conform with the standards, at least based on the examples in hand. It seems to me, that there may have been some rounding up of the dimensions on the teflon pin base part used in the base assembly. Anyway, I just wanted to post this to see if anyone else has a similar observation about the tightness in the socket for these tubes, and perhaps a warning to be careful in inserting and removing them. I have no complaints about the sound, as I said, they are wonderful.

David

Edits: 07/30/22