12bh7 in a Croft

[fiddlemaker]

Anyone know if it’s ok to use a 12bh7 in the 12bh7a positions in Croft amps?
I gather the main difference is that the “a” has a higher maximum anode voltage.
Cheers
John

[Jazid]

I think the only significant difference is the warm up time is defined in 12bh7a, otherwise ratings are identical. Also you're using it as a voltage stabiliser, not as a vertical deflection amp so any uprating to peak anode voltage wouldn't be significant.
Hope this helps.

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[Jimbo]

You can use the 12Bh7 as a substitute for the 12BH7a.

[fiddlemaker]

Thanks for the helpful replies.
Season’s greetings to all !

[Jimbo]

Thanks for the helpful replies.
Season’s greetings to all !

Merry Croftmas John:):cool:

[basnas]

Is the 12bh7 better than 12bh7a in yours Croft john

[DSJR]

If in any doubt - ASK GLENN!!!

Not saying the above will contradict others' advice here, but Glenn knows all about his circuits and has always been open to tube rolling and should be pretty unbiased in his advice on valve alternatives, whether in the supplies or the signal paths.

[goraman]

Now lets talk about substituting a 6414 for a 12BH7? I have paid less than $20.00 a matched pair.

http://tdsl.duncanamps.com/show.php?des=6414

A far better 10,000 hour computer tube.
https://www.tubesrule.com/product_p/vtu009b-.htm

[snowman_al]

Not really the same thing...

Plus the 6414 has limited anode (plate) volts of 200 max. Where you might fit a 12BH7 for a 6414, do not assume it works the other way.

Alan

[fiddlemaker]

If in any doubt - ASK GLENN!!!

Not saying the above will contradict others' advice here, but Glenn knows all about his circuits and has always been open to tube rolling and should be pretty unbiased in his advice on valve alternatives, whether in the supplies or the signal paths.

Hi Dave, I'd just rather not bother Glenn with stuff that might be common knowledge amongst those that are better informed than I am! :)


Is the 12bh7 better than 12bh7a in yours Croft john

Hi Jan, I'm not expecting a 12bh7 to be better than a 12bh7a per se, its just that I found a very nice mid fifties NOS 12bh7 available at a very good price and wanted to check equivalence/compatibility.

[goraman]

Not really the same thing...

Plus the 6414 has limited anode (plate) volts of 200 max. Where you might fit a 12BH7 for a 6414, do not assume it works the other way.

Alan

I thought they where interchangeable? Did I read right 12BH7 anode is 450 v ?

I am glad I have enough 6414 tubes to out last the amp, so I will never need to substitute.
I used to get these as little as a fiver each NOS.

[fiddlemaker]

Morning all
When looking at NOS valves terms like "pinched plate", "oval plate" and "winged plate" are often used to describe anode appearance. Is there any online resource that explains what these, and other terms mean?
Or feel free to chip in if you can enlighten me yourself :)

[Jazid]

No consistent use IMO. Usually pinched waist refers to the glass envelope of some 1950s valves that had a narrower middle, or more commonly a narrow band where it joins the base plate.

Oval anode is just anode shape, easily visible. Other egs are ladder or ribbed plate, flat plate, winged plate, and these are constructional details that indicate which production type the valve belongs to. These changed within manufacturer, across factories sometimes, and manufacturers would balance demand by selling and buying rivals bits and pieces and complete valves and branding as their own.

The details are treated fetishistically by some, truth be told the construction can make a difference to performance but so can many other more contingent factors like original performance of the individual tube, its usage history and lifetime stress, condition of getter flash, pins, and the circuit position it is used in.

In valve regulation of a PSU I wouldn't sweat these details, just make sure it meets minimum manufacturers spec ( called NOS by some but actually a slightly different thing).

Hope this helps

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[Jimbo]

No consistent use IMO. Usually pinched waist refers to the glass envelope of some 1950s valves that had a narrower middle, or more commonly a narrow band where it joins the base plate.

Oval anode is just anode shape, easily visible. Other egs are ladder or ribbed plate, flat plate, winged plate, and these are constructional details that indicate which production type the valve belongs to. These changed within manufacturer, across factories sometimes, and manufacturers would balance demand by selling and buying rivals bits and pieces and complete valves and branding as their own.

The details are treated fetishistically by some, truth be told the construction can make a difference to performance but so can many other more contingent factors like original performance of the individual tube, its usage history and lifetime stress, condition of getter flash, pins, and the circuit position it is used in.

In valve regulation of a PSU I wouldn't sweat these details, just make sure it meets minimum manufacturers spec ( called NOS by some but actually a slightly different thing).

Hope this helps

Sent from my BLA-L09 using Tapatalk

And don't forget the coatings used on the Cathode - these secret formulas were also key and most of the best ones are probably illegal to make now.