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Old 17th April 2012, 07:39 AM   #1
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Post Tesla PCC88 7DJ8 dual triode - Help Needed.

Dear Members
Has anyone tried any of these ? I want to use them in a tube pre-amplifier.
Thanks


2 x NOS -> Tesla PCC88 7DJ8 dual triode audio vacuum valves tubes röhre N0T_JJ | eBay
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Old 17th April 2012, 07:58 AM   #2
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PCC88 is a drop in replacement for the ECC88. No need to even adjust the heater voltage. Any of the millions of ECC88 circuits will do.

Shoog
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Old 17th April 2012, 08:14 AM   #3
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Thanks.
I was actually referring to the sound of these Tesla tubes.
Are they worth it ?


Quote:
Originally Posted by Shoog View Post
PCC88 is a drop in replacement for the ECC88. No need to even adjust the heater voltage. Any of the millions of ECC88 circuits will do.

Shoog
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Old 17th April 2012, 11:35 AM   #4
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Quote:
Originally Posted by Shoog View Post
PCC88 is a drop in replacement for the ECC88. No need to even adjust the heater voltage. Any of the millions of ECC88 circuits will do.

Shoog
The PCC88 has a 7 volt heater! It will work at 6.3v with reduced life and performance...
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Old 17th April 2012, 11:47 AM   #5
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Quote:
Originally Posted by vmed_cha_gr View Post
Thanks.
I was actually referring to the sound of these Tesla tubes.
Are they worth it ?
They may be worth it only if you heat then with the proper voltage, or else it would be a waste of good NOS tubes...
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Old 17th April 2012, 11:56 AM   #6
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Quote:
Originally Posted by Vincent77 View Post
The PCC88 has a 7 volt heater! It will work at 6.3v with reduced life and performance...
I have been running a pair for over 7years in my preamp at 6.3V.
So no reduced life (in fact underheating will significantly extend tube life) , and they are reputed to operate more linearly at undervoltage.

Think of them as cheap NOS ECC88, so they are a bit of a bargain (cheaper than I paid for Philips 7yrs ago).

Shoog

Last edited by Shoog; 17th April 2012 at 12:02 PM.
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Old 17th April 2012, 12:36 PM   #7
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Underheating by 10% won't do much harm, provided that the anode current is not too high. It is unlikely to do any good, except possibly a small reduction in noise.
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Old 17th April 2012, 01:38 PM   #8
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From "Getting the most out of vacuum tubes" by Robert B Tomer, page 150:

"Tubes are designed to be operated at their rated filament voltages. To get the best over-all satisfaction from their use, they should be operated as near this value as possible. However, where this is not possible, it is safer to err on the low side than it is on the high side. In other words, if they are operated at 5 to 10 percent below their rated center value, they may possibly fail to give quite as many hours of service at the remote end of their life span [...]"
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Old 17th April 2012, 02:56 PM   #9
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From valve Wizard;

Quote:
Voltage considerations: The heater voltage specified in the data sheet is the optimum value (usually specified as +/- 10%). Running them at higher voltages will considerably reduce valve lifespan and should be avoided. Running them at lower voltages, within reason, will increase their lifespan and reduce hum but also reduce their emission, although the grid curves and general performance remain much the same;- only the saturation current is reduced. Running heaters under-voltage is therefore perfectly acceptable, and provided the voltage isn't too low there will usually be no noticeable difference in sound. Normal heaters rated at 6.3V can be run quite happily between 5V and 6.9V, maybe even lower, but not higher. The exception to this rule is rectifier valves, which should not be run below 10% of their rated voltage since they usually operate very close to saturation.
Shoog
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Old 17th April 2012, 02:58 PM   #10
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Quote:
Originally Posted by Vincent77 View Post
From "Getting the most out of vacuum tubes" by Robert B Tomer, page 150:

"Tubes are designed to be operated at their rated filament voltages. To get the best over-all satisfaction from their use, they should be operated as near this value as possible. However, where this is not possible, it is safer to err on the low side than it is on the high side. In other words, if they are operated at 5 to 10 percent below their rated center value, they may possibly fail to give quite as many hours of service at the remote end of their life span [...]"
From "Getting the most out of vacuum tubes" by Robert B Tomer, page 12:

"Tubes, when operated at ten percent above their rated heater voltage, will suffer up to a fifty percent decrease in heater life. A voltage under the rated value on the other hand, while having some disadvantages as far as certain other characteristics go, tends to increase heater life substantially".

Without data, what is one to believe?

A far as the sound goes, you will need to try it in your own equipment to know for sure: 1. too many circuit variables to assign a sound to a tube, and 2. Other peoples ears are even less reliable than your own ;-)
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Last edited by Michael Koster; 17th April 2012 at 03:07 PM.
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