RnG er bare beregnet til 6DJ8-typen. Hvorfor Zigis har valgt manuel bias-justering, kan jeg ikke svare pĂĄ.
Fra ebay-annoncen:
Amp is completed with Russian 6N23P tube
can be changed to any brand 6DJ8, 6922, E88CC, ECC88 tube.
Attention – 6N1P tube can not be used in this amp!
Jeg har så prøvet 7DJ8/PCC88 også, efter lidt frem og tilbage med Zigis om, hvorvidt det var muligt (se dialogen herunder).
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Q: will RnG work with PCC88/7DJ8 tubes as well?
A: I find datasheet, this tube have 7V 300mA heater. Original is 6.3V 365mA. RnG is designed different than other amps - it give required 365mA and original tube go to 6.3V. If we send 365mA to PCC88 (instead of 300mA) voltage become 8.5V (by ohm law) way too much.
Q: So just adjusting bias will not reduce voltage to the tube? I purchased a collection of tubes, a few were the PCC88 type, and apparently are both sought after and expensive. If I can can't use them in RnG, I can probably sell them with a profit, so it is not a big problem. Just hoped I could try them out, to see why they are supposed to be so popular.
A: Adjusting bias can't do anything with heater. In tube are two independent voltages. Anode voltage make all audio job, here is biasing too. Heater voltage is independent, it is connected to simple heater spiral, heater's job is just heating cathode, for tube's proper working. If heater's voltage is too low, cathode is not enough hot and tube not work proper. If voltage is too high, everything work, however heater's live is shorter.
If you have this tube, you can try it and measure heater voltage. If voltage raise much over, say 7.5V, turn off amp and don't use this tube. I think short time (minute or so) over voltage can't burn heater.
Heater measuring is between ground (switch body, same as in biasing) and tube's pin 4. Pin 4 is near small el cap, I can try to make arrow on photo tomorrow.
Q: Is pin4 the one I have marked with red arrow?
A: Yes, this is correct pin.
Q: I have just checked 3 different PCC88 tubes. With bias for each tube adjusted to 15V (left and right), pin4 measures as follows: Tesla 7.4, Telefunken 6.8, Philips MiniWatt 7.2. These figures seemed to be stable over time. The result is a litte surprising, at least with your 8.5V figure in mind. Anyway, as all three tubes are within 10% of 7V, they appear to be usable in RnG. Or am I perhaps overlooking something here?
A: I think all thees voltages are safe to use.
I notice each tube measure different voltage, from 5.9V to 6.7V, mostly to the lower side. This was an old and very short Philips datasheet with 7V, 300mA.