ECC88 etc

[ppppenguin]

The ECC88, 6DJ8, E88CC and equivalents were used copiously in Tektronix scopes of the 545 etc era. This makes them targets for breaking for the valves which command high prices in 'phool circles.

What I didn't know until yesterday was that different makes had different heater current ratings. Fine in a 6.3V parallel cicruit but Tek had a habit of putting pairs in series. So when your 545 etc scope has an odd fault that you can't quite put your finger on you may have mismatched valves.

Unlike ECC81/2/3 the ECC88 only has 2 heater pins. ECC81 etc have 3 so they can be used in 6.3V parallel or 300mA series chains.

Incidentally, if anyone is interested in rehoming a lot of 7000 series mainframes (20+?) and loads of plugins (100+?) I know somebody who may be doing a big disposal. Money will need to change hands but I suspect it will be modest.

[Murphyv310]

Hi
The ECC88 is "normally" a drop in replacement for the rather poor ECC85, with superior performance, some radios need adjustment to oscillator and RF trimmers. Oddly the E88CC won't oscillate in FM front ends.
I'm always on the look out for ECC88s for FM tuners etc.

[Geordie McBoyne]

Pye employed the ECC88 in the tuner in the PTV portable TV set. The PCC88 was used in the tuner in the 1958 17" table model CTL58. Also, no doubt fitted n the PAM and Invicta variants made the same year.

Geordie McBoyne.

[ppppenguin]

Unlike the the EL84 and PL84, it looks like the ECC88 and PCC88 are identical apart from the heater. 7V, 300mA for the PCC88. Looking at different data sheets for ECC88, E88CC and 6DJ8, the heater current varies. At least one says 300mA. Makes you wonder why the PCC88 was needed at all, if they could make an ECC88 or equivalent with 300mA heater.

I wonder if the 'phools have latched on to the PCC88 yet.

[Murphyv310]

I've also used PCC88s in FM tuners that run 6.3v heaters with no issues.

[Mike Watterson]

Makes you wonder why the PCC88 was needed at all, if they could make an ECC88 or equivalent with 300mA heater.

Aren't there some series heater types that are not the same as same number of E series?

A reason for 7V PCC88 vs 6.3V ECC88 is likely Heater - Cathode leakage/breakdown voltage. Perhaps a higher isolation voltage needed more heater power for the same cathode temperature? Certainly if the 6.3V is at 6.3V or above within tolerance, but not at the lower limit, the PCC88 will be fine. At 10% the 6.3V range is 5.7V to 6.9V. For 7V @10% the range is 6.3 to 7.7V.

Note life of a direct filament is doubled if at 10% below nominal and halved if 10% above nominal. Hence don't put fresh Alkaline or Zinc cells into a Battery Valve set each time you go to use it. A 6V or 12V regulated DC, just slightly below the nominal voltage will greatly increase filament or heater life. Emission life is very much more complex.

The 6.3V was originally picked as 3 x 2V Lead Acid cells, which had peak of 6.9V (historically 2 x 6.9 = 13.8V for 12V car batteries). The VW Beetle in late 1950s was one of the last 6V battery system cars. Modern Lead Acid 12V batteries that don't gas on a suitable charger will rise sharply to 14.2 V after 13V is reached but drop back when charging is stopped and battery under load. Older direct filament 2V, 4V and 6V valves, certainly before 1935 would not have been intended to be used while a battery was charging; the cell or battery was taken to the cycle shop to be recharged, and if you could afford it, you had two batteries/cells.

I know there are mains series radio sets where specific valves have to be at the "earthy" end of the chain for isolation, though some Italian models ignored it. Most series mains/battery valve sets have the series arrangement for reasons of hum on mains or stability. Usually the output valve(s) are at full LT+ and the detector with audio preamp is at 0V end, with the mixer-osc next.

[Diabolical Artificer]

Some E88C's have a heater current of 325mA. Yes the audio community know about PCC88's, have done for years.

My experience with Tek 500 series scopes is that swopping valves is problematic. The time bases are very sensitive to what valve goes where.

Andy.