[JohnR]

See poll - just for fun

[JohnR]

So I got these in the post today:



The big one is a rectifier. Lights up, no reason to think it wouldn't work in a circuit once I find a plate cap large enough for it...



6.5A filament current. The small one could possibly be used in a preamp. Haven't been able to get the filament on yet.

[Tyson]

I voted but my main reason isn't listed - to me they simply sound better.

[opnly bafld]

deleted 

[JohnR]

I was hoping we could talk about something fun (for a change). Bit tired of all the bickering and attacks between people because they think something sounds better.

[Don_S]

John,  What is the size of the big one?  Need a ruler for scale. What did that monster come out of?

[Tyson]

I was hoping we could talk about something fun (for a change). Bit tired of all the bickering and attacks between people because they think something sounds better.

Ah, gotcha.  Yes, then tube rolling for me is a lot of fun.  I've actually been thinking about getting one of these amps, which is a tube-rollers dream:

https://www.ebay.com/itm/STEREO-TUBE-AMPLIFIER-INSPIRE-by-DENNIS-HAD-SET-TRIODE-SINGLE-ENDED-AMPLIFIER/153079924817?hash=item23a4464851:g:vPQAAOSwGNxbIvDZ

[JohnR]

John,  What is the size of the big one?  Need a ruler for scale. What did that monster come out of?

Aha. Didn't think of that 7" not counting the base pins. It's one of these: https://www.radiomuseum.org/tubes/tube_8020.html


It's for high voltage use, I'm really not sure what it would have been used in, TBH. Radio transmitter? This one is (true) NOS, cost me a whopping $7USD on ebay 


PS Thanks Tyson

[Tyson]

And, here's why that Dennis Had amp I linked to earlier is very exciting to me.  Check out the various tubes possible to use in that amp:

[JohnR]

Cool. That's a wide range of bias currents. Do you know what the driver tube is - 6SL7?

Oh, going there now it says "This listing has ended." Did you just buy it? 

[JohnR]

So I got these in the post today:

The small one is an Acorn tube, it's about an inch long not including the pigtail. I got it tested - the filament voltage selector switch in my TV7 seems to be flaky but I was able to use the next position. So much for tubes glowing though - at 1.25V and .1A on the filament that's only 125 mW of power, and you can barely see it glowing even in the dark.

Here's a photo of the tube being tested:

 

While the tube is tiny, the socket is larger than an octal (at top of photo). I wonder if that's part of the reason they never took off (metaphorically speaking)....

By the way, that tube (958A) is a directly heated triode... got 3 for $7 you-know-where 

[roscoe65]

Ah, gotcha.  Yes, then tube rolling for me is a lot of fun.  I've actually been thinking about getting one of these amps, which is a tube-rollers dream:

https://www.ebay.com/itm/STEREO-TUBE-AMPLIFIER-INSPIRE-by-DENNIS-HAD-SET-TRIODE-SINGLE-ENDED-AMPLIFIER/153079924817?hash=item23a4464851:g:vPQAAOSwGNxbIvDZ

Tyson,

All of Dennis' amps are tube rollers dreams.  I own two of his amps in pentode/tetrode mode.  They can use virtually any tube you can adapt into the sockets with no circuit modification needed.  The caveat is that these are two stage amps and generally need a preamp to sound their best.

My older amp is similar to the new Unversal amp, with the exception of a 6922 driver, not wired for triode, and uses a conventional tube power supply.  My newer amp is a Firebottle PSE, which is a similar amp with parallel SE output tubes, a cool isolated regulated power supply, and a 6SN7 driver tube.  This amp is plug and play for just about any output tube, putting out an easy 8wpc using 6F6 tubes up to 24 wpc or so using KT88's.  My two favorite tubes in this amp are Fivre 6F6GT's and GL KT77''s.  I am a really big fan of the 6F6's.

[Tyson]

Tyson,

All of Dennis' amps are tube rollers dreams.  I own two of his amps in pentode/tetrode mode.  They can use virtually any tube you can adapt into the sockets with no circuit modification needed.  The caveat is that these are two stage amps and generally need a preamp to sound their best.

My older amp is similar to the new Unversal amp, with the exception of a 6922 driver, not wired for triode, and uses a conventional tube power supply.  My newer amp is a Firebottle PSE, which is a similar amp with parallel SE output tubes, a cool isolated regulated power supply, and a 6SN7 driver tube.  This amp is plug and play for just about any output tube, putting out an easy 8wpc using 6F6 tubes up to 24 wpc or so using KT88's.  My two favorite tubes in this amp are Fivre 6F6GT's and GL KT77''s.  I am a really big fan of the 6F6's.

I might just buy one of the new amps.  I've got a 45 SET that I like because it's 6SN7 input tubes, and low gain (I have a high gain source and tubed preamp), so medium/low gain in the amp itself is great.  Plus is it just me, or do high gain amps tend to have a fair bit of self-noise when used with highly sensitive speakers? 

[roscoe65]

I guess it depends on the amp.  My Inspire PSE amp and LP27a preamp combo run completely silent.  The amp is a two-stage, low gain amp and the preamp is a modest gain (depending on output tube - 56 or 27) line stage.  Together they act like an integrated amp, but splitting the input stage from the output stage contributes to its silence.

On the other hand, I own a 4.5wpc 421A SET.  This amp is high-gain, with an input sensitivity of 0.65V for full output.  It is also completely silent, despite the 6SL7 input tube.  I attribute the silence partly to the fact that the 421A is an IDHT, so heater noise is less of a problem.

[JakeJ]

I added my vote.  Thanks for posting a "just for fun" thread, John!

Item number 4 is one of my favorites about tubes.  Once the filament is heated up and glowing and the plate voltage and bias voltage are settled electrons start moving from the cathode to the plate in an invisible ray that increases the signal.  Amazing really.

[fredgarvin]

I'm going to try these 717a 'doorknob' tubes in my MP 201 mkIII. I've heard good reports. Plus, they're cool.



I've been using the black can 6sj7 as drivers

[FullRangeMan]

I voted:
They glow! why electrons emission are a more musical technology than sand/silicon.
They are a reminder of a bygone era.
Because it was an era where technology was more reliable and there was no planned obsolescence.
There's lots of types of tubes.
Change the sound of the amp is not a small feature.

[JohnR]

Hah, those doorknobs are cool  Must keep an eye out for some.