Pentode/triode tubes

[firemedic]

Howdy again all, I was thinking of experimenting with using a pentode/triode preamp tube circuit since I'm chronically short on tube socket space. I'm hooked on the 5879 but what are your favorite pentode/triode tubes for guitar? 6U8s are cheap but the datasheet specifies hi-freq. usage. etc. The 7199 looks promising...

[SoundmasterG]

The 7199 was advertised as an audio tube but it was pretty much a slightly changed 6AN8A and wasn't naything special for audio. Also, these days, because 7199's were used for a lot of hi-fi amps, they are VERY expensive, and the modern manufacture of them isn't all that good. I'd go with something else myself. The 6AN8A was used in some Dynacos and Sunns, and its ok. Nothing special though. A lot of guys at AX84 were messing around with others like the 6BR8A...here's a link to the datasheet.

http://www.nj7p.org/Tube4.php?tube=6br8a

Greg

[kagliostro]

From

http://thetubestore.com/philips6u8a.html

http://lib.store.yahoo.net/lib/thetubestore/6U8A-7199.pdf

if the suggested tube to substitute the 7199 is 6U8A I think we can consider the 6U8A a tube to give a try

Kagliostro

[firemedic]

Based on the lukewarm responses on this, I'll stick with the tubes I have, and leave the major experimenting to those who know what they're doing. I haven't even used a cathode follower yet!

[leoman]

I tried the 6U8A and IMO it really has no tone.

For tone either the EF86 or the 5879 is the best pentode, the 6SJ7 is also pretty good.

The EF86 has a gain structure that no other tube has and the 5879 is close with a thicker mid but not that high end gain. The 6SJ7 isn't bad and has that Fender type sound and very useful. But nothing has the EF86 tone, you can tame it down a bit to handle any microphonic issues and not push th maximum gain, just use it more for it's tone quality.

By using the EF86 after 1/2 a 12AX7 in a SE champ type amp I was really able to get that Marshall sound out of the amp. Something no matter how many extra gain stages I could not.

[DummyLoad]

6CM8 looks interesting...

--DL

[echuta13]

6GH8a as well.

[tubeswell]

By using the EF86 after 1/2 a 12AX7 in a SE champ type amp I was really able to get that Marshall sound out of the amp. Something no matter how many extra gain stages I could not.

Ditto - I have done exactly the same thing with a parallel SE amp

[Fresh_Start]

By using the EF86 after 1/2 a 12AX7 in a SE champ type amp I was really able to get that Marshall sound out of the amp. Something no matter how many extra gain stages I could not.

Ditto - I have done exactly the same thing with a parallel SE amp

Not the same thing, but that is a neat circuit Tubeswell.  On the pentode/triode tube path, dropping the tremolo and using a 6BM8 for the triode & power tube might be an interesting low-power design.

Cheers,

Chip

[tubeswell]

By using the EF86 after 1/2 a 12AX7 in a SE champ type amp I was really able to get that Marshall sound out of the amp. Something no matter how many extra gain stages I could not.

Ditto - I have done exactly the same thing with a parallel SE amp

Not the same thing, but that is a neat circuit Tubeswell.  On the pentode/triode tube path, dropping the tremolo and using a 6BM8 for the triode & power tube might be an interesting low-power design.

Cheers,

Chip

But I love tremolo! 

[jojokeo]

6bl8 is another one to try.

I tried the 6U8A and IMO it really has no tone.

For tone either the EF86 or the 5879 is the best pentode, the 6SJ7 is also pretty good.

The EF86 has a gain structure that no other tube has and the 5879 is close with a thicker mid but not that high end gain. The 6SJ7 isn't bad and has that Fender type sound and very useful. But nothing has the EF86 tone, you can tame it down a bit to handle any microphonic issues and not push th maximum gain, just use it more for it's tone quality.

By using the EF86 after 1/2 a 12AX7 in a SE champ type amp I was really able to get that Marshall sound out of the amp. Something no matter how many extra gain stages I could not.

+1 leoman
I've made at least 5 different ef86 & 8 or 9 pentode preamps in various configurations to date. They are so much fun to play around with and offer a tone and several ways of varying gain adjustments that you can't get w/ using only triodes. One of my favs in tone and versitility is cascading pentodes. But, I haven't tried something like tubenit's pentode follower yet, only an ef86 followed by a somewhat normal CF stage using some of Merlin's suggestions also.
Why not try a 6bl8 or 6an8a or = and try the pentode follower? tubenit loves it's smoothness and seems worthy to give it a go. If not, make adjustments until you find something you like - no big deal.

[kagliostro]

Why don't try with a different approach

V1 = Triode + V2 = pentode ?

Kagliostro

[Fresh_Start]

That Selmer sure is an interesting circuit!

How about:

Triode => cathode follower => TMB tone stack => pentode => poweramp

Might get some of that compression from the CF that tubenit likes so much, plus the pentode getting hit relatively hard...

Chip

[38Super]

But, I haven't tried something like tubenit's pentode follower yet, only an ef86 followed by a somewhat normal CF stage using some of Merlin's suggestions also.
Why not try a 6bl8 or 6an8a or = and try the pentode follower? tubenit loves it's smoothness and seems worthy to give it a go. If not, make adjustments until you find something you like - no big deal.

Was thinking about amp input signal connected to parallel input stages, EF86 and 12ax7 capacitor coupled into a linear pot mixer to allow either gain stage or a blend to drive later stages.  Maybe, might be better to have a 12ax7 gain stage, followed by paralleled stages as above?  Probably, some tweaking would be necessary to try to get gain similar between pentode and triode stages.

Any merit?


rob

[bigdaddy]

I'm leoman I signed in with an older login by mistake....

I got the idea from the Matchless to use the pentode after the 12ax7 but found that you only really need a 12AY7 and not in parallel. It offers so much gain without driving the next stage crazy like adding too many 12AX7 stages does and IMO is a tone suck.

Also the squish control as some call it can be setup more like a gain control and you can go from more VOX like tones to the Marshall sound with that high end sizzle no other amps get. The EF86 is all about how you set it up, so many variables. And I found that the EH worked well, maybe an original Mullard would sound better but for the money the EH was fine. I even did a dual EF86 preamp with a SE EL34 power section that was amazing, you have so much control over the gain structure. It's like you can have 100 knobs on the preamp and all of them actually work.

[tubeswell]

FWIW some clips of me accompanying 'self on Strat with that EF86 SE amp (with Celestion G10 greenback and running a 6L6G off a 5U4GA) that I posted the schematic for earlier:

Earlier variant with a 5F2A tone stack:

Trem:

http://www.nzguitars.com/forum/download/file.php?id=8232


Blues:

http://www.nzguitars.com/forum/download/file.php?id=8258


Variant with the big muff tone stack (as per the schematic)

Trippy trem (with steel slide):

http://www.nzguitars.com/forum/download/file.php?id=8343


Blues:

http://www.nzguitars.com/forum/download/file.php?id=8346


Mangling Jimi Page:

http://www.nzguitars.com/forum/download/file.php?id=8347

[jojokeo]

Was thinking about amp input signal connected to parallel input stages, EF86 and 12ax7 capacitor coupled into a linear pot mixer to allow either gain stage or a blend to drive later stages. Probably, some tweaking would be necessary to try to get gain similar between pentode and triode stages.
Any merit?

I've designed pretty much just that same idea for/with someone on this forum. There's several itterations of it but haven't had time to build and explore it yet. Been waiting for feedback from him on any progress to date. Each section has it's own independant vol and gain controls, and can be paralleled or cascaded. For him it's a smaller SE design but I also have other PP versions using the same pre.
Now that a few birthdays, holiday, travel, gigs, & other events are out of the way I'm refreshed & excited to get the creative juices flowing and start building again.

[jojokeo]

Also the squish control as some call it can be setup more like a gain control and you can go from more VOX like tones to the Marshall sound with that high end sizzle no other amps get.

I used the squishy control in my first ef86 amp and was very underwhelmed by it so I removed it and went w/ something else. Maybe I'll try it again some day since I have a much better feel and understanding of the tube (or any pentode for that matter) now?

[firemedic]

Man this is a hot topic. My experience is that I have built only 4 amps- 3 of them featuring 5879s somewhere in the PA.
One is a TOS.
One is a Super Reverb using a 5879 input tube on the normal channel, then 1/2 of the reverb send socket to recover after the tonestack; it sounded pretty dull so I replaced the 5879 with a paralleled triode 12AY7- huge improvement. I fixed it so I can bridge the channels together - 3 paralleled input triodes! and it is amazing.
My little SE 6V6 amp sounds the best & it uses a 5879 for the input tube->tonestack->paralleled triode 12AX7->6V6, but I really think the paralleled triode is the key here. One triode can be switched off & when it is, it just doesn't sound as good. Per Merlin, the input stage drive signal is too weak to really drive a pentode right & I'm inclined to agree.
I'm tempted to switch stages (paralleled triode as input tube), so the pentode gets more drive signal, in the SE amp but it sounds so good now, I'm going to put it off.

[bigdaddy]

The first time I used a squish control I was like big deal. Then by accident it worked, it works a lot better when it's not the first stage for some reason. It's really something you have to experiemnt with. Those pentodes are little pieces of gold if you want to get away from the normal either Fender/Plexi sounds we all are so familiar with. So far the EF86 is #1, next the 5879 and then the 6SJ7. I had a great sounding SE amp with a 6AT6 into the 6SJ7 with a 6L6GC output. It didn't sound like any amp I ever heard but still had a bit of that Fender thing happening, good tone.

But if you want that high end IMO no other tube can do it better then the EF86. And set up right there aren't microphonic issues. If you go past certain parameters then you have problems. But just use it to get that sizzle without the feedback other tubes have when trying to get that. For anybody who ever used a 100 watt Marshall stack on 10 with a Les Paul you know what I am talking about. The sound right before the fuses are supposed to blow but the transformers do instead..

[zendragon63]

I am in a little late here; I have tried and actually like either the EF86 or the 6BR7 on the second stage. To my surprise, I really,really like the slightly driven EF86 flavor. YMMV.

Merlin's points out in chapter 3 that "...more versatile tones are possible if the pentode is operated at sensible gain but is proceded by at least one gain stage." is good advice, especially if you looking for a little bit of that special sauce earlier in chain. 'Sensible gain' meaning a much lower plate and G2 resistor loads shooting for the knee of the curve rather than the traditional Vox values. It did reduce the microphonics on ALL of my pentode preamp builds. I have tried it pentode-driving-triode and triode-driving-pentode and I gotta say that the latter gives up the goods. Be prepared to fiddle around with the values on RP, RG2 and RK to get 'it'.

Squish controls really didn't float my boat but you might find them to your liking. There are several posts on the pentode preamp designs and alot of great insights from PRR.

+1 on the neat circuit tubeswell. Regards

dennis

[kagliostro]

I've just find the schematic of a modulator that uses a triode pentode tube + the final tubes (no PI as there is an interstage transformer)

Kagliostro

[echuta13]

I always thought the Gibson GA1RVT was a pretty novel amp.  It use a 6BM8 for output/trem, a 7199 for reverb/preamp first stage, and a 6EU7 for reverb recovery/preamp second stage.  Would be pretty easy to use more common tubes like a  6AN8 or 6GH8 for the 7199, and a 12AX7 for the 6EU7 if you were so inclined...

[Fresh_Start]

I always thought the Gibson GA1RVT was a pretty novel amp.  It use a 6BM8 for output/trem, a 7199 for reverb/preamp first stage, and a 6EU7 for reverb recovery/preamp second stage.  Would be pretty easy to use more common tubes like a  6AN8 or 6GH8 for the 7199, and a 12AX7 for the 6EU7 if you were so inclined...

That is an interesting circuit.  http://www.el34world.com/charts/Schematics/files/gibson/GA-1RVT.pdf

Has anyone played through a GA1RVT?  The reverb/mix control looks strange to me but I think I understand how it works.

Cheers,

Chip