Alternate tubes to 300B?

[rbc3]

Are there drop-in alternates to 300B that will work in the Paramount in place of 300B?  I found a few interesting tubes below but not sure if they'll work in Paramount.  Are there others?  What modifications, if any, would be required to use these in a Paramount?

32B
http://www.elektronenroehren.de/avvt/datashts/av32b.htm

PX25M
http://www.elektronenroehren.de/avvt/datashts/PX25m.htm

5B
http://www.elektronenroehren.de/avvt/datashts/av5b.htm

8B
http://www.elektronenroehren.de/avvt/datashts/av8b.htm

300B XLS
http://www.emissionlabs.com/datasheets/EML300B-XLS.htm

320B XLS
http://www.emissionlabs.com/datasheets/EML320B-XLS.htm

 

[Paul Birkeland]

32B

Would probably work, but hard to find.

PX25M
http://www.elektronenroehren.de/avvt/datashts/PX25m.htm

Not a good idea, will not work.

5B

Will operate in the amplifier, may need some bias tweaking.

8B

No curves, hard to say.

300B XLS

May work, draws more heater current than a 300B, may need to add a cap to nudge up the filament voltage.

320B XLS

Even worse than the 300B XLS, probably not a good idea.

 

[rbc3]

I'm getting really interested in the 32B since it looks like it can put out more watts if given more plate voltage.  In the Paramount, will it behave like a normal 300B or can it drive a higher watt output?

 

[Paul Birkeland]

Yeah, the 32B has an uprated plate voltage rating, as well as higher plate dissipation.  You'd want to take advantage of both to get the extra power out of it.  Unfortunately, the plate curves on the webpage you linked to and the characteristic data provided are a poor match (one or both are wrong).  An operating condition is listed at 400VPK, -58V bias, and 95mA, while on the curves, 400VPK and -58V bias gives more like 500mA.

To get significantly more power out of the Paramount, you would need a new power transformer (for more voltage), a new plate choke (that could handle 100mA), and a new output transformer (to handle the higher power).

This isn't impossible, but it will be expensive, and you'll end up with something that isn't a Paramount and will no longer take 300B's.

 

[rbc3]

Hrm, not sure why the mismatch between the characteristic data and the plate curves.  I'll see what I can find out about that.  So I take it then in the Paramount the 32B will operate like a normal 300B and put out the standard wattage.

 

[rbc3]

I reached out to the owner of the 32B web page and he confirmed that the plate diagram is correct and the characteristic data has a typo.  It should read 400VPK, -85V bias, and 95mA.  He has corrected the characteristic data on the page.  Does that change the answer about whether or not it will work in a Paramount?  Is it a drop in equivalent to a 300B or will I need to do something to the Paramount like tweaking the bias?

Thank you,
Robert

 

[Paul Birkeland]

Do feel free to try the tubes in the Paramount, then post the voltages on your 4 pin socket.  We can then make accurate recommendations on whether rebiasing is advisable.

-PB

 

[rbc3]

Now that I have my Paramounts back up and running, I finally got to try these 32B tubes out.  Here are the voltage readings on the pins.  I've also included the voltage readings in the other Paramount with the stock 300B Electro-harmonix tube.

AVVT 32B
A1 : 72V
A2 : 441V
A3 0V
A4 : 67V

EH 300B
A1 : 75V
A2 : 440V
A3 : 0V
A4 : 70V

Pretty darn close!  I guess that means it doesn't need any bias adjustment.  I went ahead and powered the 32B up and went through the hum balance adjustment before powering my speakers.  What's interesting about these tubes is that they read 0V when measuring and adjusting the hum balance pretty much through the whole dial of the potentiometer except the very ends where it is .1V.  I suppose that means this is an insanely quiet tube!  The best I've gotten out of other 300B tubes after adjustment is .3V.  Most of my 300B tubes at their best spot on the hum balance pot are between .5V and .7V on my multimeter.

A quick comparison on the sound of these tubes is that the bass is slightly a little less explosive as on my Svetlana Winged C tubes.  The clarity and details are astounding.  The highs are wonderfully crisp without being painfully sharp.  The mids are amazing and vocals seem to float through the room!

I don't have any Western Electric 300B tubes which people say are the gold standard.  However, between the sets of tubes I have, there's absolutely no desire to spend that kind of money because the ones I have sound fantastic.  No need to go further to my ear.  Although I do have a pair of Sophia Princess Mesh tubes on order, so we'll see how those are in comparison.  However, all the tubes I've purchased don't equal the cost so far of one set of WEs...  These are my most expensive pair at $550, thanks to the cheap Euro!