When I find I have replaced a tube the second time, I go for the schematic and read voltages and resistances. In all cases this has not been a problem. It just seems to me that the tube does not last long.
The most recent example is in an HRO 60. Agreed they run the plate with, what I call, excessive plate voltage---250 volts. I am sure they followed the tube manufacturers specs on it, but like the Collins situation, they could have reduced it. The screens are at 85 volts. 73 Jim de W5JO ----- Original Message ----- From: "Brett gazdzinski" <[EMAIL PROTECTED]> To: "'Discussion of AM Radio'" <amradio@mailman.qth.net> Sent: Thursday, June 24, 2004 6:55 AM Subject: RE: [AMRadio] 6BE6 > I don't know. > But some tubes always test on the weak side on my tube tester, I think > it's the settings for that tube type being off, as every tube does maybe > 70% tops. > Other tube types may get up to 90%... > > Running tubes to hard will cause them to fail, excessive plate voltage, > screen voltage, plate current. > Cathode resistors going low, shorted/leaky cathode bypass caps? > > Funny, because I have found the small tubes in receivers to work fine > At 100 volts or less, no need to strap them. > > The 6C4 in my homebrew receiver (local osc) works fine as low as 30 volts! > I run it at 105 volts, but don't need to, and above about 75 volts > gives very little extra output. > > > Collins used to advertise they ran the 75s series at 150 volts to reduce > heat and > extend the life of the tubes... > > Maybe run a test, and see just what the tubes are running at voltage and > current wise... > > Brett > N2DTS
