Quote:
Originally Posted by microstrip
I also bought a large stock of the same type PCC88 Philips with codes DJER 4F and 4G. I have measured about 10 and they are in general low noise and both triodes are matched in gain and DC - an important parameter as the sections work in parallel in my LP275s. From these 10 only one had one noisy triode in the low frequencies - it is now burning-in for a few days, as I have found that some tubes that are initially noisy become silent after 50-100 hours burn-in.
Measuring a few used noisy ECC88/6922 I have found that their triodes were significantly unbalanced. Probably tubes in these conditions will ear out much faster as the tube current does not split equally between the triodes.
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That is good that they have acceptable measurements and that a good proportion of them are usable. Thanks for reporting the codes. I would think 4F = 1964 June, and 4G = 1964 July.
You have inspired me to check the codes on my tubes more closely. I have found that on some of them, the second row of codes is just barely visible and almost readable with a magnifying glass and a flashlight.
Under the DJER row, mine seem to have a row with three characters starting with a partial circle character, followed by 4H. I think the partial circle character must be this one for "Elektronski Industija, Nis, Yugoslavia":
I would think the 4H would be 1964 August.
Anthony