Submini tubes: 6N21B vs 6N17B pinout

[cab42]

I am building a F-2B tube preamp with a submini tube using Vigilante397's Particle Accelerator board.

Super easy build! All part are in place except for the tube and I am getting all the correct voltages at the test points. I had it running for 12 hours with rock stable voltages. So far so good!

But tonight when I wanted to install one of my 6N21B's, I found out that they were actually 6N17B's.

As the pinouts are different, I just wanted to check whether my pin to pin conversion is correct and I haven't missed something obvious (my first tube build). Pinouts (from russiantubes.com)

6N21B: 6N17B:

2N21B	2N17B
9	5	Anode 1
8	3	Grid 1
6	2	Cathode 1
10	4	Heater 1
4	1	Anode 2
3	7	Grid 2
1	6	Cathode 2
5	8	Heater 2

Does that look OK?

And a quick bonus question: I am using a 1590B for the build. How much ventilation do I need? I had planned to drill a pattern of holes above the tube or in the sides of the enclosure. Would that be enough?

[iainpunk]

those pin conversions look good

the filaments generate about 2.5W for most sub-mini tubes, i don't think it needs any holes, since the metal case would conduct enough, but if you want you could add a slot or some holes above the tube.

cheers, Iain

[vigilante397]

I agree with Iain, everything looks good to me My newer submini builds actually use 6N21B because they're cheap and easy to find. I like milling ventilation slots in my boxes, and it's not a bad idea to throw a couple holes in the box to let heat out. Also with that much current in the filament they glow nice and bright, so it's neat to be able to see them too

[MetalGuy]

Does that look OK?

6N21B's pin 2 is an internal shield that goes to ground but will work without it as well.

[cab42]

Thanks Iain and Nathan

I felt so confident that I just went ahead and finished it earlier today. And it worked on first power up!

I haven't had much time to play with it, but it sounds great!

The treble pot may bad, though. The sound starts to get more and more distorted/gated after 3 o'clock and then cuts out. When turned all the way up the sound returns.

Nathan, it was such an easy build. It almost felt like cheating, using your board 

I have a hybrid amp, solid state preamp and tube power amp, and I am looking forward to try my new preamp directly into the power amp.

I'll drill some holes in the enclosure. Slots looks great, but demands skills and tools that I'm not in possession of.  A straight line of fairly big holes could look nice. Or maybe increasing size along the line?

[cab42]

Does that look OK?

6N21B's pin 2 is an internal shield that goes to ground but will work without it as well.

Yeah, Nathan noted that in the build doc. But I used 2N17B, and it only has eight pins.

[vigilante397]

Thanks Iain and Nathan

I felt so confident that I just went ahead and finished it earlier today. And it worked on first power up!

I haven't had much time to play with it, but it sounds great!

The treble pot may bad, though. The sound starts to get more and more distorted/gated after 3 o'clock and then cuts out. When turned all the way up the sound returns.

Nathan, it was such an easy build. It almost felt like cheating, using your board 

I have a hybrid amp, solid state preamp and tube power amp, and I am looking forward to try my new preamp directly into the power amp.

I'll drill some holes in the enclosure. Slots looks great, but demands skills and tools that I'm not in possession of.  A straight line of fairly big holes could look nice. Or maybe increasing size along the line?

Excellent, glad you got it together so quickly And I'm glad you liked the board, I actually stopped offering PCBs because a couple people (literally 2) were having trouble getting them working and I don't have time to help everyone troubleshoot since I make a lot more money selling pedals than I do PCBs

As for the sound cutting out on the treble, it's a known issue I fixed in version 3 of my builds, and it's only an issue when gain and treble are both turned up. You can generally get away with turning up one or the other without issue.

I think I still have a handful of these PCBs lying around since I stopped selling them, so if you want any more to build for family/friends/customers let me know

[vigilante397]

I'll drill some holes in the enclosure. Slots looks great, but demands skills and tools that I'm not in possession of.  A straight line of fairly big holes could look nice. Or maybe increasing size along the line?

I forgot to mention, a line of holes would definitely look cool, and increasing size along the line would be SUPER cool. Either way I'd love to see what you come up with

[Marcos - Munky]

I have a hybrid amp, solid state preamp and tube power amp, and I am looking forward to try my new preamp directly into the power amp.

You'll be so pleased. My main clean amp is all tube, using this preamp (but with a 6N2P as the tube, no submini). My original idea was to build something else and, after testing some stuff, I gave this preamp a try. It just sounds amazing!

[cab42]

You'll be so pleased. My main clean amp is all tube, using this preamp (but with a 6N2P as the tube, no submini). My original idea was to build something else and, after testing some stuff, I gave this preamp a try. It just sounds amazing!

I gave it at test this afternoon. It sounds really good!! You are absolutely right. I am pleased!

My amp (Guyatone Flip 2000 MkII) is born without an effects loop so I did a quick and dirty one a while ago by desoldering the cable from the master volume to the power amp board and inserted send and return jacks. Unfortunately that means I can't use the spring reverb. I need to move the insertion point to a more suitable location, but that's a subject for another thread.