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A list of tubes suitable for DIY projects

76.24.78.116
Posted on December 26, 2013 at 08:29:28
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Thought it would be a good idea to start a thread and go through tubes that would make excellent audio tubes. The idea is to come up with tubes that are still easily available, not overly expensive, and outside of the mainstream of the 12AX7/12AU7, 6922, EL34, 6550/KT88, etc.

Many of the common tubes rely on new production tubes that can cost dearly and are of questionable pedigree/reliably.

Some ones that quickly come to mind are the 807/1625 family, 12SN7/12SL7. 6S4, 12B4, and 7058.

After listening to a couple amps that use the 1625 tube as an output stage, that pretty much convinced me that if one is going to use tubes to listen to music, these type of tubes are the way to go. Keep the cost of the tubes down, and spend the cash on other items that improve the sound, such as better caps, resistors, transformers, chokes, etc.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

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    ...
not exactly cheap, but available, posted on December 26, 2013 at 09:50:01
FenderLover
 I like the 5687.

 

RE: A list of tubes suitable for DIY projects, posted on December 26, 2013 at 10:38:41
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Freo

I love the 6AH4.
Beats the 6S4 and 12B4 hands down.

DanL



 

+1, posted on December 26, 2013 at 11:27:06
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 6AH4GT +1 as a Finals tube etc., and it can be driven beautifully by 1/2 a 12AX7 or 1/2 of a 6SL7WGT, two stage DC amp !!

I have schematics for same in BOTH P-P and in SE, Contact me off line if you wanna see 'em.

Biggest bang for buck IMHO is a 6AQ5 / 6005 triode connected, 9 Watt max plate dissipation when trioded, a lively firecracker. 6AH4GT, unlike 6AQ5, is a real triode, 7.5 Watt rated plate dissipation, run either at 62% of rated dissipation, Golden Ratio.

Dems the two, de bees knees dude.

Jeff Medwin

 

RE: A list of tubes suitable for DIY projects, posted on December 26, 2013 at 11:56:07
thermionic addictions
Audiophile

Posts: 894
Joined: June 16, 2006
 The 6V6 or the loctal version, 7C5 which is the one I prefer.
NOS 7C5's can be bought for $10 or less and are a very good sounding
tube. I have only used them in triode mode but I'm sure they would
sound good as a pentode as well.

Cal

 

RE: A list of tubes suitable for DIY projects, posted on December 26, 2013 at 12:49:23
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Some great suggestions so far. I'll have to look into the 6AH4 tube. I have used the 5687 tube with excellent results. Also used 6085 tubes back when you get them cheap, which is also a really nice audio tube.

What about higher power output tubes? I remember an amp that used 6KD6 sweep tubes for outputs that sounded pretty good. The only issue I've run into is that a lot of the pentode tubes need to have a separate screen supply so as not to over drive them, which means no ultra liner configuration.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

Low g2 voltage limitation of most sweep tubes doesn't preclude UL operation...., posted on December 26, 2013 at 13:02:23
Steve O
Audiophile

Posts: 12374
Location: SE MI
Joined: September 6, 2001
 ...However, it will require an OPT with a tertiary winding specifically for g2. Not common these days but a custom winder should be able to come up with something suitable if you really have your heart set on sweep tube UL.

 

4P1L is all I need, posted on December 26, 2013 at 16:38:30
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 My amp is 4P1L transformer coupled to PSE 4P1L, all in triode filament bias. Simple as that.

I've only used directly heated tubes for several years now.

 

UL pentode, posted on December 26, 2013 at 16:39:04
thermionic addictions
Audiophile

Posts: 894
Joined: June 16, 2006
 Paul Scearce posted a schematic for a UL pentode amp here awhile
back. A simpler amp you probably wont find and uses the 6BQ5, another
favorite tube for the DIY crowd.

If you are looking for lots of power the Russian GM70 would be a
good choice, these tubes were fairly cheep at one time but prices
are rising. Still an affordable tube. Kevin Carter at K@K audio
has done some wonderful work with this tube.

Cal

 

403b, posted on December 26, 2013 at 18:18:18
Salectric
Audiophile

Posts: 1358
Location: East Coast
Joined: February 23, 2003
 A Western Electric 403b (strapped for triode) makes an excellent driver in my 46 SE amp. The gain is just enough when loaded with a plate choke or IT, and it is quiet and sounds great. Best news is that it is readily available for less than $20.

 

Good point. That was the case with 6146 amps.., posted on December 27, 2013 at 06:49:50
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 I had read that the theater amps of the 50's used 6146 tubes, and a with a tertiary winding was used for those units. Given the high costs of the current 6550's, the 6146 is worth another look as well.

The 5933 also looks like it could be a good option. You could run a quad of those with the old HK Citation II output iron and get some great sound.

A buddy of mine is looking at using a quad of 1625's with the Citation II iron. Should be interesting to see how that turns out.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

You mean as an input/preamp tube, Dan?~nT, posted on December 27, 2013 at 13:44:48
Cleantimestream
Audiophile

Posts: 7551
Location: Kentucky
Joined: June 30, 2005
 ~!
The Mind has No Firewall~ U.S. Army War College.

 

RE: You mean as an input/preamp tube, Dan?~nT, posted on December 27, 2013 at 16:26:27
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Good for preamp or driver use.
Mine is in the preamp.

DanL



 

RE: Good point. That was the case with 6146 amps.., posted on December 28, 2013 at 10:42:21
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 RCA M-12182 and Altec 1530s both used the 6146...RCA recommended changing them to 6550s..What I did on my 1530s was change them to GEC TT-21s and then I was able to change the pair of OC3s to OD3s and that took G2 to the 300v I needed for the screens.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: A list of tubes suitable for DIY projects, posted on December 29, 2013 at 09:44:04
Palustris
Audiophile

Posts: 2408
Location: Cape Cod
Joined: September 12, 2008
 This is my list of "audio" tubes. I made this "cheat sheet" as an easy reference to pick a tube for a particular application e.g., for a particular gain or transconductance. Note the 46 and 59 are triode connected and the 27, 37, 56, and 6P5 are all roughly equivalent to the 76.




 

RE: A list of tubes suitable for DIY projects, posted on December 29, 2013 at 13:01:33
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
 Look for non-six volt versions of popular tubes. The 1625 certainly qualifies. One that comes to mind is the 8BQ5. These were mostly used in TVs and the supply greatly exceeds the demand. Peruse the RCA Receiving Tube Handbook or other sources for more non-normal heater voltage variants on otherwise normal output tubes. You may have to design and build your own heater supply, but that gives you the opportunity to make it DC which is always a plus.

 

6AH4 looks like a excellent line-stage tube, posted on January 3, 2014 at 11:49:52
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Thanks for the input. I think I'll get a 6AH4 line-stage preamp put together.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

RE: 6AH4 looks like a excellent line-stage tube, posted on January 3, 2014 at 13:06:34
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Freo

I use a rechargeable 9V on the cathode
About 120V B+ and a plate choke
Cap couple the output
Or use a 136C Hammond Interstage

DanL



 

RE: 6AH4 looks like a excellent line-stage tube, posted on January 3, 2014 at 13:43:36
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Sounds good.

I'm going to use a design I found online. This one uses TV damper tubes for rectification. It's going to use a inter stage transformer to lower the impedance and provide excellent drive to the power amp.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

RE: 6AH4 looks like a excellent line-stage tube, posted on January 3, 2014 at 14:11:13
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002

Freo

If this is the schematic then
you will have a gain of 2.5.
Is that enough?

DanL



 

Sure. Should be OK, posted on January 3, 2014 at 14:19:16
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 A gain of 2.5 from a 2 volt source is more than sufficient.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

RE: Sure. Should be OK, posted on January 3, 2014 at 14:35:00
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Freo

On further investigation ...
1( It is used at a non-linear area.
2) It is at 83% of it's max power.
The bias is at 24V for a preamp,
that is driver territory.

IMO
Drop the UF4007s and just use 2 6AX4s
(Center tap to ground)
Change the cathode resistor to 300R
More linear and the tubes will last
Bias is still 7.5V - more than enough

DanL



 

RE: Sure. Should be OK, posted on January 3, 2014 at 14:40:05
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Freo

BTW PS Parts -
Caps here

http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/25-5-MFD-370-VAC-OVAL-DUAL-RATED-RUN-CAPACITOR-27L629-22-1225.axd

Chokes here

http://www.tubesandmore.com/products/P-RC-2

DanL



 

Thanks! Parts are on the way. , posted on January 3, 2014 at 14:48:37
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Dan,

I already ordered the chokes and transformers from Heyboer. The caps have been ordered as well. Once all the parts are in, will lay it all out and send the chassis out to get painted.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

Wwell, it's finished, posted on July 6, 2014 at 14:50:57
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008



It took a lot longer to get it done than originally planned, but the project is finally completed.

Some mods were made to the base design: Khomozo stepped attenuator (Takmen REX upgrade) in the front, Heyboer chokes and output transformers, and a slightly different power supply cap setup are the major deltas. The tubes were all DC'ed, and 6DE4 dampers were uses for the power supply.

The sound from this preamp is outstanding. Significantly better that the vast majority of 6DJ8/12AX7/6SN7 units. Will post pics of the inside soon.
" Don't look back. Something may be gaining on you"

Satchel Paige

 

RE: Wwell, it's finished, posted on July 7, 2014 at 16:53:28
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008



Here is a picture of the underside:
" Don't look back. Something may be gaining on you"

Satchel Paige

 

Low Mu tubes are the way to go!, posted on July 9, 2014 at 18:30:30
Freo-1
Audiophile

Posts: 1329
Location: Florida
Joined: June 14, 2008
 Best sounding preamp I have heard to date.

" Don't look back. Something may be gaining on you"

Satchel Paige

 

RE: A list of tubes suitable for DIY projects, posted on July 15, 2014 at 08:51:39
hifipaul
Audiophile

Posts: 735
Location: NY
Joined: December 22, 2008
Some unusual suggestions; 6CK4 (10w triode), 6KN6 (sweep tube), 7AF7 (gain/driver), 6C5 (gain/driver), WE396 (G/D), 6BG6 (sweep tube), 76.

All of the above are good sounding and inexpensive.

 

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