Yes indeed Jim you're quite correct to point out this misleading ambiguity! I'd fallen victim to this inadvertent corruption of meaning in my desire for brevity. Thanks for the spot-on elucidation he
All good points you make here Jim. When it comes to the small desktop amps like the SB220 and TL922 having separate filament transformers I find that inserting a pair of GE CL-60 NTC thermistors in e
You're probably quite right Bob; I guess I'm a believer in an ounce of prevention is worth a pound of cure :-) Besides, I quite like the way the initial turn-on filament glow now rises up in a nice s
That's right Pete, the SB220 had a well designed filament transformer that self-limited the cold inrush current to a safer value close to what the tube manufacturer Eimac specified. What the NTC ther
Hi Jim, With the TL922 filament xfmr I use one CL-60 in each leg of the primary winding. The second one is probably not necessary but I put it there because it allowed me to fine-tune the filament vo
That's right Don; and combining the requisite drive power attenuation with some NFC imparts several benefits; especially so with multiple paralleled tube amplifier configurations. Leigh VK5KLT Proper
Roger, that's because you have a very well-designed amp that behaves itself and responds benignly with whatever's thrown at it.... :-) Leigh VK5KLT That is the problem. With the power turned down, th
Excellent solution Bert: always guaranteed to work and set a hard-limit on the misbehaving / overshooting rig's max power output; and ensure that the Po can NEVER go above what it is set for to drive
Hi Dan, Not that it matters much, but are you absolutely certain that the current 3CX800/3CPX800A7 tube products sourced from CPI are not of Chinese origin and instead supplied to CPI under an OEM ou
Yes indeed Dick....instant-on thoriated tungsten filament tubes are nice! But alas, the rather pricey 3CX1200 can't be second-sourced :-( Leigh VK5KLT Or better yet, one or two 3CX1200's. 73, Dick, W
That's right Roger, the suffix has undergone a few revisions...it was a 3CX1200A7, then a 3CX1200D7, now it's a 3CX1200Z7. I think the improvement iterations related to internal grid construction dif
Good comments here Bob; you've nailed some relevant points here. The GS35B does indeed need a higher plate voltage / plate load impedance to achieve parity in efficiency with the 8877; complaining ab
Hi Bill, But my point here was that if you design the tank circuit for a higher plate voltage and plate load impedance then you won't have to take a hit on the efficiency. As Jim reported in his repl
Hi Carl, But this is a technical forum for homebrew amplifier builders and experimenters, so why do you continually make repeated reference to commercial amplifier companies in your posts? I agree th
Carl, there's nothing at all wrong with posting to both forums in this instance as the subject matter here about the problematic dearth of current production Tx tubes is equally pertinent to the inte
That's right Peter; agree in respect of triodes...tetrodes where plate current is relatively independent of plate voltage might be a slightly different matter. However a well designed amp will not ne
Mark, another possibility for this anomaly might be the small grid current noticed at keying up the rig is attributed to imperfect carrier balance in the rig's balanced modulator allowing some Tx car
Yes, the ACOM-1000 and ACOM-2000A are two good examples of what good amp designers can do with good tubes. These GU74B tube based amplifier products have been immensely successful for ACOM and others
Agreed Carl; but the labelling is unimportant. Quibbling over whether the tube's plate dissipation is 600W or 800W is rather pointless. It's a function of air supply CFM anyway as the cathode emissio
Carl, VK land has a 1 kW power limit on the HF bands. However I would not use a single GU74B/4CX800A tube at more than 800W PEP. Run at that Po level or under, in SSB mode the damn tube lasts forever