Silvertone 45A tubes....rare variant

[jmillerdoc]

Hello,
I have a chance to purchase a pair of Silvertone 45A tubes right now for $175. Problem is with these tubes (as I have researched) is they are totally different than a standard 45. They are larger (almost the size of a 2A3) and have a rated power output of 3 watts. The problem I have with them is knowing how to test them. They have a max plate voltage of 325v unlike the 45's lower one and the person selling them has tested them on a tester that shows they are just below acceptable for a regular 45 tube. This is testing them as a 45 though and I am not sure if they are good or bad. The guy seems to think they are good and don't test correctly for a 45 b/c they really are not like a regular 45. What to do. They are very rare tubes and not much is out there about them. They were apparently an attempt to bridge a gap between the 45 and a 50, from what I have read.

Does anybody out there know anything about these that might lead me to believe they are still in good working order even though they don't test good as a 45 tube?

I was planning on trying them in my latest 2A3 build.

Thanks,
Jeff

[HollowState]

Originally Posted by jmillerdoc

Does anybody out there know anything about these that might lead me to believe they are still in good working order even though they don't test good as a 45 tube?

From what I can gather from searching the web and from my own printed sources, the 45 and 45A are similar in some respects. The same filament and the same transconductance. The plate dissipation is greater, hence the larger bottle. The ability to put more power in will get you more power out, all else being equal.

I believe these tubes should test like a 45, or very close to one. It's human nature to question test results when one has something potentially rare and valuable, especially if there is any ambiguity at all. However as with all tubes, and especially directly heated filament types, there is an acid test seldom mentioned or done by sellers. This is the dropping of filament voltage by 10% or "life test" as it is sometimes known. Doing this under test will tell you a lot about the condition of the tube's emission capabilites. Directly heated filaments react quickly to this test. A tube that falls back a lot, is soft and acts "spongy" to a reduced filament is a weak tube. Conversely, one that only falls back a little and seems hard is a strong tube.

This is a judgement call that one has to make honestly with any power tube. It also helps to have a little past experience with testing to develop a mental curve of what is acceptable and what is not. But a weak tube will show itself right away by falling back excessively to a 10% filament reduction. So what's excessive? Well, a strong tube will hardly drop or perhaps fall back 5% to a 10% reduction. A weak tube will fall back in excess of that. Typically 20 to 30%.

Perhaps you can ask the seller to perform such a test. Personally I would not spend that kind of money on old used tubes even if they are "rare". I'd add a few dollars more for new tubes like the Sophia mesh plate 2A3s or their 2½ volt 300Bs.

[jmillerdoc]

Who makes a 2 1/2 volt 300B? That sounds interesting. Do they work well?

I appreciate the advice. I think my money is better spent on a couple of more pairs of good used 2A3's I have been buying up. Thanks for the advice, I am going to pass on these. I don't even have a 45 amp built yet. When that happens I will concern myself with the 45 tubes. I already own several pair I can't use yet anyway.

Glad I asked, I was really close to getting them.

Jeff

[boywonder]

JJ also makes a 2.5V 300B equivalent.... the 2A3-40


6moons audio reviews: JJ/Tesla 2A3-40

[HollowState]

Originally Posted by jmillerdoc

Who makes a 2 1/2 volt 300B?

Sophia Electric makes them. I've never used them. I only know they exist. I have heard amplifiers that use their tubes, like one of the Cary's. There is also an Asian made preamp that uses their 2A3 mesh plate as an output driver. I heard that at the last New York Audio Rave I attended. Sounded great! You can see it sitting on the floor in the 5th picture down.
Zu Audio House Party Tour
Sophia Electric Tubes