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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=[email protected]> 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=[email protected]> 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.

Bob W4JFA?

On Mon, Jul 15, 2024, 1:23 AM Robin Midgett via <RobinK4IDC=[email protected]> wrote:

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