I have been looking on the internet and have been able to find some of
the differences between old power tubes. Is there anyone here who can
clear up some fine points for me.

I have a tube amp that uses 6BQ5/EL84 power tubes. But the manufacturer
says I can also use 7189/7189A's. I think I understand the difference
between these tubes; but I also run into variants that number E84L and
some that talk about the 7320. Is there anyone who can tell me about
the E84L and the 7320 vis-a-vis the EL84/7189A? Thanks.

jrlanders

http://www.nostalgiaair.org/tubes/

Will give you direct-substitutions and some of the subtle differences.
Of that class, some are listed as power-pentodes, and some as
beam-power tubes. There are issues with backward-compatibility (amps
set up to a 7189A will not necessarily accept a 6BQ5 without some
modification... if at all), but most amps set up for a 6BQ5 will accept
the 7189(A), 7320, EL84. Note the base diagrams as shown on that site.

But the above information is only at the most superficial level. How
much further you wish to go is up to you.

When you do sub, make sure that you address any bias issues as may
arise.

Peter Wieck
Wyncote, PA

in article LejPf.601290$084.172071@attbi_s22, Jim Landers at
wrote on 3/7/06 12:17 PM:

I have been looking on the internet and have been able to find some of
the differences between old power tubes. Is there anyone here who can
clear up some fine points for me.

I have a tube amp that uses 6BQ5/EL84 power tubes. But the manufacturer
says I can also use 7189/7189A's. I think I understand the difference
between these tubes; but I also run into variants that number E84L and
some that talk about the 7320. Is there anyone who can tell me about
the E84L and the 7320 vis-a-vis the EL84/7189A? Thanks.

jrlanders


This may not be 100% accurate but should be operationally useful:

The 7189A is similar to the EL84, but can withstand a higher plate & screen
voltage. In most circuits you can substitute a 7189 for an EL84, and adjust
the bias.

The old US made EL34s withstand higher plate voltages and currents than
modern production. Vintage amps were typically geared for 115 or 117 VAC
but the mains voltages you usually get are in the range of 120-125 VAC in
the US, which increases the B+ voltage. This may push vintage amps with
vintage tubes outside of their safe operating area. The result might be an
orange plate and hastened failure.

Thus if you stick a modern EL84 in a vintage amp designed for that tube,
often the plate voltage may be excessive. Therefore, it is usually a good
practice to use 7189s in vintage gear to replace the EL84s.

Having said that, some of the current production 7189s won't withstand the
higher voltages either.

To add to the confusion, EL84Ls are essentially 7189s that can withstand
high plate voltages - maybe 375 or 400 VDC (if memory serves me right).

The Russians make an inexpensive tube that is essentially a 7189 or an EL84L
called the 6P14EP. These can be used instead of 7189s, etc. but the pinouts
of the Russian tube may require that you jumper two of the pins on the tube
socket for it to work.

I don't have much experience with the 7320, but you can go to Frank's Tube
website and download and compare the specs on the different tubes:

http://www.tubedata.org/


Jon

Peter wrote

http://www.nostalgiaair.org/tubes/

Will give you direct-substitutions and some of the subtle differences.
Of that class, some are listed as power-pentodes, and some as
beam-power tubes. There are issues with backward-compatibility (amps
set up to a 7189A will not necessarily accept a 6BQ5 without some
modification... if at all), but most amps set up for a 6BQ5 will accept
the 7189(A), 7320, EL84. Note the base diagrams as shown on that site.

But the above information is only at the most superficial level. How
much further you wish to go is up to you.

When you do sub, make sure that you address any bias issues as may
arise

Duncan Munro's free TDSL gives substitutes, but only where they are similar in
nearly all respects. However, it enables searching by characteristics for
finding similar valves which are not direct substitutes, and lists brief
essential data in columns for ease of comparison.

TDSL is available from the font of all valve knowledge:

http://www.duncanamps.com/

PSUD is good too.

Duncan himself has gone very quiet...

cheers, Ian