[Amps] Cetron 811a.

[Ulf (SM0NOR)]

Thanks for the advice.

Only tuning of the input circuit left. Then ready for the test.... :)

73's

Ulf (SM0NOR)
ulf at sm0nor.com



On 6 dec 2011, at 19:13, Eddy Swynar wrote:

> Hi Ulf,
> 
> Well, I can only speak of my own personal experiences here with a 4 x 811A amplifier that I built here some 31 years ago...FWIW!
> 
> First-off, I used surplus tubes in mine---so take what I say with a grain of salt, or ignore it altogether. 
> 
> (1) One of the  811As that I purchased had, unknown to me, an internal short from the grid to to the filament: the moment I applied power to it, the grid meter pegged itself, & I had to get a new one. Lesson learned: check all of the electrodes for shorts BEFORE installing the tube.
> 
> (2) When I initially attempted to run all 4 tubes under load in the amplifier, the very second I hit the key I noticed that the plate of one tube would appear redder than the rest---then in seconds it would turn yellow, then white, and then a small hole the size of your smallest fingernail would appear right in the middle...and a fuse would blow. Lesson learned: MATCH each individual tube for resting current. Failure to do so will cause a "discrepant" tube to "hog" the load, & it'll self-destruct in short order.
> 
> I can't even recall now how many 4-pin coil forms I ended-up getting out of that exercise, before I learned the importance of matching tubes for resting current! But again, these were all surplus jugs that cost me probably two bucks a pop ("pop"---literally!), so the lesson---though still rather expensive back then---didn't exactly break the bank...
> 
> One more step to do as a precaution might be to "bake" the tubes for an hour, or so, with just their filaments on---no plate voltage. I've never done this personally, but have read that it's a good idea with surplus stock...
> 
> There you go, Ulf---at least ONE taker to your query, so far...
> 
> ~73!~ de Eddy VE3CUI - VE3XZ
> 
> 
> 
> *****************************************************************
> 
> 
> On 2011-12-05, at 5:36 PM, Ulf (SM0NOR) wrote:
> 
>> No takers?
>> This ought to be a very simple question :)
>> 
>> 
>> 73's
>> 
>> Ulf (SM0NOR)
>> ulf at sm0nor.com
>> 
>> 
>> 
>> On 4 dec 2011, at 11:23, Ulf (SM0NOR) wrote:
>> 
>>> Hi all,
>>> 
>>> I recently bought 4 Cetron 811a from Nebraska Surplus, date coded 1988.
>>> I intend to put them into a home brewed amp that is real close to smoke testing.
>>> Is there any start up procedure that is recommended for NOS 811:a? I have not come across any recommendation regarding this so far. But before, I put them in and apply filament and HV, I thought i'd ask here.
>>> 
>>> Thanks!
>>> 
>>> 
>>> 73's
>>> 
>>> Ulf (SM0NOR)
>>> ulf at sm0nor.com
>>> 
>>> 
>>> 
>> 
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