[Moon-net] How to recognize a tube's degradation

[Bergonti, Sergio]

A bit late but better than never... I fully agree with your report Eddy. 10dB with such tube it is almost unbelievable @ 1296, it will be tough to have it with a '327 which has more ears than the rugged 347.  Even if I run my 327 at a some higher idle current than you do, below a certain drive power it really trips off.  I work with G2 at 550 Volts, to get the kW out the current is pretty low around some mA, 4.2Kv anode loaded. I guess that the TV guys used to ran these tubes at 600mA or more for proper linearity and at lower freqs, of course.

73s Sergio ik2mmb


-----Original Message-----
From: moon-net-bounces at list-serv.davidv.net [mailto:moon-net-bounces at list-serv.davidv.net] On Behalf Of Eddy Jespers
Sent: Thursday, October 18, 2007 8:14 PM
To: Koellner, Guenter (NSN - DE/Muenich); moonbounceboard
Subject: Re: [Moon-net] How to recognize a tube's degradation

Hi Günter,

In regards of your TH347 amplifier, your power gain is outstanding. You 
achieve more than 10 dB gain. My best tube i have, gives me 8 dB only on 
1296. I believe 10 dB is possible when you have a perfect tube, which 
probably you have.

Measure IG2. In my amp i have a stabilized 600 VDC supply for UG2, at full 
output i measure up to 60 mA IG2. The original design of the Plisch 
amplifier is designed for maximum 30 mA or so. Probably your G2 power supply 
is limiting the maximum RF output. G2 is the "gain control" of the amp.

In my setup i have 4KV on the plate, -95VDC UG1 for 150 ma IA idle, -150 VDC 
UG1 for cutoff, together with grounding G2 for cutoff.

I need around 350 watt of drive for 2KW output.

So, when your G2 supply is not able to deliver the nessesary 60 -70 ma, the 
tube will cut off at a certain input power.

I did not test using different IG1 versus gain, in my setup i can only vary 
UG1 +/- 10 VDC for bias setting.

Best 73's Eddy ON7UN
www.on7un.net

----- Original Message ----- 
From: "Koellner, Guenter (NSN - DE/Muenich)" <guenter.koellner at nsn.com>
To: "moonbounceboard" <moon-net at list-serv.davidv.net>
Sent: Wednesday, October 17, 2007 8:21 PM
Subject: [Moon-net] How to recognize a tube's degradation



Hello,

first, some thanks to all the hints that I got for my oscillating amp chain. 
Actually it was just too much total gain with too less screening. I did not 
notice that the transverter was the input and part of the oscillation chain, 
too. Despite of course all methodes of preventing this, just selectively 
enabling bias for the stages and observing their output power would help.

Well, all that effort was in order to get some more drive power for my 
TH347.

Before, I had about 75W and got 950W output from it. Measured safely with a 
power meter that I aligned with my HP436 meter. So I think that there is no 
measurement error. The bias was very high set at 300mA.

Now I am getting around 110W of drive, but not more drive power. With 50mA 
bias, I just get 850W, and only when setting the bias to 300mA, I am getting 
100W more.

According to HB9BBD's note, I checked the heater voltage and probably was a 
little bit too much in the past, just 0.2V too much. Don't know if this is 
the reasons.

How can I understand if this less output power is a result of a degraded 
tube? What does degrade? Gain or maximum power? My tube never has seen an 
arc, and it was always ran with less than its maximum power (just due to a 
lack of drive). Could it be that the capabiltiy of emmitting electrons 
became degraded over time? I do not think that the gain has become less, 
even different, this tube is showing much more gain than many others that I 
have heard from.

Thanks for your comments!

73, Günter (dl4mea)

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