I note the large cathode area.
Suggests this tube type can supply a lot of peak cathode current.
According to this Philips datasheet the PY88 can supply a maximum peak/pulse current of 550 mA and a maximum of 175 mA as steady current. The power needed for the heater of the PY88 is 0.3 x 26 = 7.8 Watt.
For comparison: The UY85 can supply a maximum peak/pulse current of 660 mA and a maximum of 110 mA as steady current. The power needed for the heater of the UY85 is 0.1 x 38 = 3.8 Watt.
Links to Philips datasheets for these two tube types:
PY88 Philips
UY85 Philips
For me the conclusion is that the PY88 is not a tube that stands out for the amount of peak cathode current it can supply given the amount of heater power that is needed. I am pretty sure this is the result of the fact that there is more distance between the heater and cathode of the PY88 than there is distance between the heater and cathode of a 'usual' rectifier like the UY85.
That the the cathode area of the PY88 is large(r) is in my view the result of the larger distance between heater and cathode. The larger the distance between heater/center and cathode, the larger the cathode area will be.
Also note that the ratio of maximum peak/pulse current and maximum steady current differ quite a lot for these two tube types: 3.24 for the PY88 against 6 for the UY85.
As a booster diode the PY88 fulfills a different role than the UY85. The frequency that a PY88 sees in its designated role in a TV is to rectify voltage pulses at (in most cases) a frequency of 15,625 Hz coming from the horizontal deflection transformer. The UY85 rectifies (in most cases) a mains voltage of around 220 V at a frequency of 50 Hz.
For comparison: The UY85 can supply a maximum peak/pulse current of 660 mA and a maximum of 110 mA as steady current. The power needed for the heater of the UY85 is 0.1 x 38 = 3.8 Watt.
Links to Philips datasheets for these two tube types:
PY88 Philips
UY85 Philips
For me the conclusion is that the PY88 is not a tube that stands out for the amount of peak cathode current it can supply given the amount of heater power that is needed. I am pretty sure this is the result of the fact that there is more distance between the heater and cathode of the PY88 than there is distance between the heater and cathode of a 'usual' rectifier like the UY85.
That the the cathode area of the PY88 is large(r) is in my view the result of the larger distance between heater and cathode. The larger the distance between heater/center and cathode, the larger the cathode area will be.
Also note that the ratio of maximum peak/pulse current and maximum steady current differ quite a lot for these two tube types: 3.24 for the PY88 against 6 for the UY85.
As a booster diode the PY88 fulfills a different role than the UY85. The frequency that a PY88 sees in its designated role in a TV is to rectify voltage pulses at (in most cases) a frequency of 15,625 Hz coming from the horizontal deflection transformer. The UY85 rectifies (in most cases) a mains voltage of around 220 V at a frequency of 50 Hz.
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Maybe a bit "off topic" but I used the booster diode PY81 as a delay (30 to 50 seconds, depending on the date of production) in my Aikido headphones amplifier. The amplifier passes about 55 mA of current, so well inside the safe area of operation of the PY81 (maximum steady current = 150 mA). I also designed this amplifier such that the PY81 only sees 46 V difference between its heater and cathode.
I consider this build as my finest (until now...).
Link to the details: Headphones Amp Finished
I consider this build as my finest (until now...).
Link to the details: Headphones Amp Finished
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Thanks, Robert!
The PY88 heater power ist even more than you mentioned, it's 0.3 A × 30 V = 9 W. And yes, it's a conclusion of the large isolating gap, required to withstand pulse voltages of several kV in booster/damper diode applications.
Best regards!
The PY88 heater power ist even more than you mentioned, it's 0.3 A × 30 V = 9 W. And yes, it's a conclusion of the large isolating gap, required to withstand pulse voltages of several kV in booster/damper diode applications.
Best regards!
Did you parallel the anodes, and use two 6AX5 for rectification role (given your comparison is related to half-wave damper diodes that would require two devices) ?
Are you also assessing the hot turn-on diode current capability when comparing, as the damper diode datasheets typically don't include that rating ?
Just on the off-chance, does anyone have a data sheet for 6P22C? I think the Roman equivalent is "P", the original Cyrillic looks like an "H" with the horizontal bar slid all the way to the top. The source of all thermionic data (Frank's site) doesn't have it. I recently bought a pair of amplifiers made to the GEC 88-50 circuit using these (top cap cathode) rectifiers and they proved to be rather interesting with a very slow warm-up time that is kind to the amplifier's (NOS KT88) output valves.
WRT to prolonged cathode warm up: I've always been thinking the higher heater power doesn't only help to cope with the big heater to cathode gap, but also to keep warm up time within the range of the other tubes, especially the horizontal deflection power tube. The booster/damper diode provides the only plate current path to this tube, and it would be highly dangerous for the screen grid when no plate current flows for some longer time.
Best regards!
Best regards!
It's all about mass and RC thermal time constants. Higher heater power implies more mass. But a high Vhk voltage rating implies poor coupling (higher R) between heater and cathode, increasing the RC time constant, and also requires more heater power. I suspect my 6P22C have a deliberately high mass cathode sleeve (C) in order to increase the thermal time constant without needing more heater power.
And what does this poor sweep tube screen grid think about that?
The European 6P22C equivalent is EY88, isn't it? So I guess both heater powers are the same?
Best regards!
The European 6P22C equivalent is EY88, isn't it? So I guess both heater powers are the same?
Best regards!
@jcalvarez: Thank you so much. The Svetlana data sheet includes a lot of hype, but the technical stuff looks plausible.
My guess is that the PY88 at first had a voltage rating of 26 V at 0.3 A.
Besides the Philips datasheet I linked to, also see this data:
Data PY88
But for sure this data could be wrong. See as an example the multitude of mistakes I found in this handbook:
List of Errors in Electronic Tube Handbook Muiderkring
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The AVO valve tester setup manuals were notorious for mistakes and it's always a good idea to check their settings against a manufacturer's data sheet before switching to "Test". If you think about it, third party manuals were type-set but not checked by someone who felt they had a personal/company interest in them being correct. And it's amazing how errors creep in...
No, I use only one 6AX5 per rail. It works fine for the low (195V 20mA) rail and the tube will probably last forever due to the low current but it seems I'll need something heftier for the 250V 90mA supply so I bought a few EY88's from eBay.
Unless I change my mind again the rectifier lineup will be: 2x 6AU4GTA for the output tubes, 2x EY88 for the drivers and 1x 6AX5GT for the input tubes.
Possible changes would be to use EY500/6D22S instead or 6AU4GTA just for the top caps (I like the look of tubes with top caps...) and 2x EY81 instead of the 6AX5, again for the top caps and to raise the voltage a bit to allow additional filtering.
One of the major mistakes in the "Electronic Tube Handbook" by Muiderkring is that for a substantial part of the small signal triodes the cut-off voltage for the control grid is stated instead of the control voltage which fits the plate voltage and current as depicted.
Radiomuseum.org corrected this misinformation on their site. But the internet is still filled with this kind of misinformation.
You can power 2A3 PP Amity design in mono-block configuration with two EY88 ( one channel ) - it's beeen done locally and works for years so far as i know.
Sounds good!
Most reports I've read about using damper diodes as rectifiers states mentions a very long life time.
By the way, I ordered some EY81s yesterday for the input stage PSU. A bit of extra voltage headroom for an additional RC section felt like a good idea.