Re: Ten-Tec Centurion, new tubes, idle current, glowing plates?
|
If the zener is shorted the idle current goes way higher thsn 125ma. ?So I doubt it’s shorted.
On Monday, July 15, 2024, 9:10 PM, Chuck Neal <cdoneal@...> wrote: That negative bias is sometimes done with a zener in series with the CT od the filament transformer.? When that goes, no negative bias.? I’ve seen that many times, since zeners are not very good in handling higher currents. -Chuck ? From: ham-amplifiers@groups.io [mailto:ham-amplifiers@groups.io] On Behalf Of Chuck Neal via groups.io
Sent: Monday, July 15, 2024 9:06 PM
To: ham-amplifiers@groups.io
Subject: Re: [ham-amplifiers] Ten-Tec Centurion, new tubes, idle current, glowing plates? ? Sounds like two problems at once ? 1) Plate meter is reading low, perhaps due to a burnt shunt resistor in the metering circuit ? AND ? 2) Bias supply is not working depending on the plate voltage in that amp.? Not familiar with that amp’s plate voltage but “zero bias” tubes like 3-500’s do need some minimal bias, like 5 – 8 V negative, again depending upon plate voltage. ? -Chuck K1KW ? ? If your plate meter reads 125 ma at idle the tubes are immediately dissipating 375 watts with no drive. ?Immediately turning red on the bottom bell at 375watts is a bit quick. ?Are both tubes turning red about the same way or is one brother red thsn the other? ? ? On Monday, July 15, 2024, 10:59 AM, Robin Midgett <RobinK4IDC@...> wrote: "Over time the bottom Bella of the tube will definitely turn red even with no drive." The brand new tubes did this right out of the box...no time elapsed. ? On Mon, Jul 15, 2024, 8:35 AM Louis Parascondola via <Gudguyham=aol.com@groups.io> wrote: Oh Sorry, normal idle current is 125–160ma. Over time the bottom Bella of the tube will definitely turn red even with no drive. ? On Monday, July 15, 2024, 9:27 AM, Robin Midgett <RobinK4IDC@...> wrote: Thanks for the info, Louis. To be clear, the photo you're referencing is from Bob W4JFA, not from me or my amplifier.? My tubes from Tom Rausch of CTR Engineering do have white bases. On Mon, Jul 15, 2024, 5:36 AM Louis Parascondola via <Gudguyham=aol.com@groups.io> wrote: The tube in that photo, does that tube have a white base to it?? It looks like there is no white base and the white looks to be a reflection of the filament light.? If this is so, that tube didn’t come from Tom at CTR.? Normal idle current on a pair of those tubes is around 125ma give or take a few.? THE PLATES WILL GET RED FOR SURE LIKE THAT OVER A PERIOD OF TIME.? That would be normal.? I’m not sure however if that amp has electronic bias ? I know it has QSK but I think you can switch between PTT and QSK.? Tom tests all his tubes ?do if they are new the amp should be working normally.? But the tube in the pgmhoti doesn’t seem to have any white base on it at all unless the photo is deceiving. ? On Monday, July 15, 2024, 4:48 AM, Bob <W4JFABob@...> wrote: I hope the attached picture shows. This is a 3-500z with approx 90 - 100mA plate current after about 60 - 90 seconds. ? I'd like to query the collective knowledge about a Ten-Tec Centurion amplifier I've been working on, if you'd be so kind as to respond: I found that one tube had a cathode to grid short. I ordered and received a new pair of 3-500ZG tubes from Tom at CTR Engineering. I installed the tubes and it makes power. With the amp keyed into a dummy?load & no drive, I see an indicated plate current of ~125mA, which I think is normal for a pair of 3-500Z tubes?in grounded grid; please comment on that. More to the point, the bases of the tube plates glow a dull red in that condition. I've been told by an elmer who I'm inclined to trust that the plates shouldn't glow with only 125mA plate current, and if they are glowing in keyed/idle, then the indicated plate current is likely false & for some reason greater than 125mA. The original fault that I found is one tube has a short between grid and cathode, the other tube doesn't show any shorts. Is it possible or likely that some of the resistors used to derive?the plate current indication were damaged by the shorted grid/cathode condition? If the plate current is greater than 125mA, what would cause that? I'm aware that Ten-Tec had some problems with bias from the QSK board in these amps for a time, but I don't know anything more about that. Any info is appreciated. I recorded these parameters on each band; measurements taken from the front panel meters of the amp. I stopped at 1kW output because I don't have a slug for my Bird 43 that will indicate above 1kW on HF frequencies.? Band | Load | Tune | Pin | Pout | Iplate ma | Igrid ma | 160 | 10 | 8 | 80 | 1kW | 600 | 180 | 80 | 10 | 5 | 55 | 1kW | 630 | 140 | 40 | 10 | 2.5 | 80 | 1kW | 440 | 160 | 30 (40) | 1.6 | 0.75 | 50 | 1kW | 450 | 160 | 20 | 6 | 0.75 | 50 | 1kW | 500 | 170 | 17 (15) | 7.4 | 1.25 | 60 | 1kW | 630 | 160 | 15 | 6 | 0.75 | 80 | 1kW | 530 | 160 | 10 | 5 | 0.5 | 75 | 1kW | 600 | 160 |
|
Join ham-amplifiers@groups.io to automatically receive all group messages.
