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In the Forum: Melquiades Amplifier
In the Thread: Single-stage Melquiades vs. DHT amps

Post Subject: Type 45... they're not all the samePosted by floobydust on: 6/16/2009

Romy,

I have a very large collection of 45 triodes.... many brands and varying internal construction. From my humble viewpoint, here's some personal findings on the various types:

- Globe 45 tubes... these are the earliest, mostly from RCA. There are two basic internal constructions, one with all glass/wire supports and the later version with a mica insulator on top. In short, I don't like these. All of my samples (about 6) have higher hum level output compared to later ST-style types and all are more sensitive to mechanical vibration than ST-style as they lack all support sans the wires that hold the elements in place. They are pretty however.

- ST-style glass. I have samples from RCA, Sylvania, Philco, Tung-Sol, National Union, General Electric, Ken-Rad... maybe another, but I can't think of any more off hand. What I've found is that the internal construction is more important than name branding... and that many manufacturers commonly sourced tubes from each other for economical reasons... i.e., the expense of settting up the line for any given type. Note: I actually have two new RCA branded 45 tubes in original boxes with matching date codes on the bases. Yet, they are completely different internal construction. One is made by RCA and the other by Sylvania... who knew. The same applies to other brands... they did source from each other frequently. In short, the brand name on the tube does NOT validate any authenticity of the manufacturer.

As for internal construction, my preferred one is actually made by Sylvania. Also note that they also made a few internal variations over the years. The better Sylvania 45 has a top mica which is circular, but two sides are cut flat and parallel to the anode. They also have 3 rivets holding the vertical metal rods (to the mica) for support and also have two wire braces that extend from the ends of the top mica to the glass to reduce mechanical sensitivity. Shown below a (rough) picture of the top.

Note that later versions (probably cost reduction) eliminated the support rivets and the lateral bracing wires... I have some of these as well. While I don't really discern any sonic difference, I feel that the more robust internal construction will hold up better over time without becoming loose. I've found my preferred Sylvania versions marked commonly as Philco, Ken-Rad and the "solo" RCA. I also match them into pairs based on internal construction, (brand and date code second, but preferred) along with gain, hum balance, distortion and output power. Hope this helps. Oddly, the RCAs consistently have a higher hum level (on AC filaments) than most of the others.

Regards, KM

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