Mike -
I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds
up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets
'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass
seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes
to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise
in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep
trying tubes until you get a 'good' one.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Mike Bryce wrote:
I wonder.....
when drake assembled the radios, did they go through three or fours tubes per radio to get one
that worked correctly?
dosen't seem logical. And although you can't argue with the fact that the subing out the tube
fixed the problem, I wonder if there is something hidden down someplace in the design that causes
the problem
just a thought
Mike, wb8vge
On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote:
Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those
alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to
get one.
The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to
6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for
many years before these symptoms appeared.
Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s
in the future, while I can get them. For sources I've seen that have both, the price is the same.
73,
Randy WB4SPB
----- Original Message -----
*From:*Al Al <mailto:[email protected]>
Out of curiosity, how many 6EH5 tubes did you have to go through to find a
good one?
Al, n7ioh
Payson, Arizona, USA
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