Cathode follower resistors?

[tubenit]

I am going to try an experiment today just for the fun of it ............  (supposed to have heavy storms all day)

I'm wanting to see what difference it would make having the tone stack before the 5879 pentode? So I thought I'd try a CF approach to that idea.

What values would you try for the resistors that I have indicated.  The red one and the pink one?

I've never understood what difference it makes having the pink cathode follower resistor be a higher or lower value than the preceeding triode plate resistor?

With respect, Tubenit

[rzenc]

Cool!!!
I will start a kinda TOS build and was fooling around with this idea too. However, i was planning to experiment with the following arrengment:
OD stage: dual ganged pot for gain control and drive control- triode gain stage coupled to CF - drive control - 5879 - pentode/triode morphing as tone control - output level pot control

I will use a ganged pot for gain and drive controls because I will strip a orange dual terror and build the TOS inside. It has only 6 pot holes and chassis space is very limited. Will use 6005 as output power tubes.

Looking forward to know how it turns out!
Congratulations for your adventurous spirit and continuous amp development!

Best Regards
Rzenc

[bobmegantz]

Since you know the grid voltage (it's DC coupled from the previous stage), you choose the cathode resistance for the desired quiescent bias current (the cathode voltage will be a couple of volts higher than the grid voltage).  You can then draw the load line and see what's up.

The load for the previous stage is chosen in the normal way (based on that stage's desired conditions).

[tubenit]

This was one of the coolest and most fun experiments that I've done. And successful too! And it didn't take too long since I had a spare V2b triode already.

It's not a better tone but it is quite different than the TOS which has more of the Dumblish tone.

The tone stack works "better" in front of the 5879 pentode then behind the pentode. It sounds like it has a wider ranger or sweep from treble to bass. And the "bass" doesn't sound as muted meaning the bass sounds clearer and more articulate.

Probably 75% of the TOS wah/vowel tone is gone. However, the harmonics are unbelievably sweet sounding now and there is a Marshally crunch that sounds excellent to me. The harmonics are signficantly more pronounced now to my ears.  I think Geezer's HoSo56 amp design had this type of sweet harmonics to it.

The sustain is about the same, I would say.  It still blooms but not into the vowel tone. The notes just simply swell and head into sort of a musical feedback.

IF I had heard this amp & didn't know anything about it:

I'd describe it as a very musical harmonically rich Marshall tone with a smooth crunch to it with the chording & rhythm.  It has more of the ZZ Top Marshall & some of the Joe Bonamassa Marshall type tone to it.

I'd say it is easier to hear each note in the chording with this wiring compared to the original TOS.

However, playing lead with single notes and double stops, etc ............ it sounds more like a blend of a Marshall amp with the Dumblish sustain.  The notes hold great and have very musical sweet harmonics and they still swell into a sustain. The vowel tone is mostly gone.  The best way I can describe it, is I am getting the kind of sustain that I got from the Plexi 25w and Plexi 50w amps I built using a good tube screamer.  Except again the harmonics are much richer sounding to my ears with this amp.

In summary, with chording and rhythm ......... I think someone might mistake it for a really sweet musical sounding Marshall amp.  With playing lead, I think it sounds more Dumblish but with a loss of the vowel/wah tone.

The amp has more of a smooth crunchy tone and less creamy vowel tone.

That's probably the best I can describe it. My guess is that I'll leave it this way? I'll have to play it with the band first to make a final decision. I am anticipating that the chording with this amp will cut thru the mix just perfectly.

I honestly think if someone came to me and asked me to build a Marshall type amp but with more sustain and mids, this is probably what I'd try to get them to consider.

I posted the SCH schematic and layout here:

http://www.el34world.com/Forum/index.php?topic=11455.new#new



With respect, Tubenit

[tubeswell]

IF I had heard this amp & didn't know anything about it:

How about a soundbyte then?

[tubenit]

How about a soundbyte then?

Oh, I definitely intend to do one and post it.  

With respect, Tubenit

[jojokeo]

1) the harmonics are unbelievably sweet sounding now and there is a Marshally crunch that sounds excellent to me. The harmonics are signficantly more pronounced
2) The notes just simply swell and head into sort of a musical feedback.
3) a very musical harmonically rich Marshall tone with a smooth crunch to it
4) it is easier to hear each note in the chording
5) The notes hold great and have very musical sweet harmonics and they still swell into a sustain

Now those are attributes that I love!!! Embellishing the guitar's and player's tones together clearly & accurately w/ the harmonic magic that only driving tubes the right way can provide. 

[rzenc]

Hi nit

Are you using a 12AY7 or 12AV7 on the C.F. ? Hard to tell from the .gif schem... Well I ask this because TUNG SOL quotes 12AY7 and GE quotes 12AV7 maximum heater to cathode voltage as high as 90V max on both data sheets

http://www.mif.pg.gda.pl/homepages/frank/sheets/127/1/12AY7.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12AV7.pdf


.... and with 150K on cathode I wonder whether it it close enough to it?
If it is that close to 90V between heater-cathode, elevating heater reference is necessary.

I used Merlin's loadlineplotter with your values and got around 110VDC @ C.F. grid... Can you confirm this?

Hope this helps
Best regards

Rzenc

[tubenit]

Yes, I am using a 12AY7 with the CF. 

I have NO idea what the voltages are?  And I also have not gotten around to trying any other 12A_7 tube there yet.

The chassis is back in the head and I may not have time to get it out this wk?  Next time I remove it, I'll try to record and post voltages. 

with respect, Tubenit

[Tone Junkie]

More good work T.
Thanks Bill

[tubenit]

Guys,

I played the amp some more yesterday and it sounds great! So there is no tonal need to change anything ..............but ...........

For no other purpose than to satisfy my own curiousity, I am thinking about connecting the CF to the 5879 pentode. It should only take me about an hour to convert to that.

Would this be the correct way to connect a triode CF to the 5879?

And has anyone already tried this?

With respect, Tubenit

[sluckey]

That should work just fine.

[Fresh_Start]

tubenit's original question was about the plate resistor of the preceding stage and the cathode resistor of the cathode follower.  Bob got it right in terms of biasing the preceding gain stage however you want it, then use the resulting plate voltage to bias the cathode follower.  

However, no one has talked about the bias of the cathode follower and how it relates to the compression/distortion generated by a tube triode cathode follower.  Merlin discusses this on his website and more thoroughly in his preamp book.  An overly short summary is that decreasing the value of the cathode follower's cathode resistor increases the compression effect but here's the website discussion

It makes perfect sense that adding the cathode follower would make the tone more Marshall-esque.  After all, Marshall uses a cathode follower before the tone stack in virtually every circuit.

I'm curious about whether or not the later circuit with the cathode follower after the pentode has any impact on the effects loop.  It's a passive loop, but now there's a buffer driving it when the overdrive is engaged.  What's that going to do?  I don't know...

Cheers and many thanks to tubenit for continuing to share his experiments,

Chip

[jojokeo]

However, no one has talked about the bias of the cathode follower and how it relates to the compression/distortion generated by a tube triode cathode follower.

An overly short summary is that decreasing the value of the cathode follower's cathode resistor increases the compression effect

I'm curious about whether or not the later circuit with the cathode follower after the pentode has any impact on the effects loop.  It's a passive loop, but now there's a buffer driving it when the overdrive is engaged.  What's that going to do?  I don't know...

I was wondering why/how no one responded or commented also. Halving the load resistor's value gives more and (in some people's minds) better gain!

I like the effect it's had on my 6BM8 CherryBomb amp (mini-bassman - inspired) that I installed it on.

It's effect on the effects loop should be a definite improvement. I am wondering about the protection part of the CF that's omitted with being okay for tube life/reliability?

*tubenit - the 330k screen resistor on the 5879  will yield a fairly high headroom response since the ratio normally btwn the load & screen resistor's are usually 5:1 (you likely know this but I thought I might point it out anyway just in case).

[Fresh_Start]

jojo is referring to the diode, grid stopper resistor, etc. shown in Merlin's "preferred" DC coupled cathode follower.  See link above.  Seems like cheap insurance to me.

Cheers,

Chip

[jojokeo]

agreed! IIRC it had to do w/ the cathode-grid voltage rating of the tube not being exceeded and causing arcing or blowing it out?

[tubenit]

I experimented with this. And my initial impression is this amp has the best harmonics, sustain and bloom of any that I have built. It sure gave me a "wow" response playing it.

This does NOT have the Marshall crunch that the CF after V2a had. However, it has incredible sustain and blooming. The notes are both smoother and clearer (not cleaner) sounding than NOT using the CF after the 5879.  The harmonics are excellent. It sounds more Dumblish but with less vowel tone and perhaps more creamy/smoothness then the Tweed BluezMeister.

It does NOT have the vowel/wah tone that the original TOS had. Not sure why, but that is just about gone.  

However, it does have the creamiest smoothest OD of any of the TOS variations.  I find myself turning the trim to about 7 and turning the drive to about 3 and then the level to about 6 for my favorite tone.

I have not had time to A/B it with the Tweed BluezMeister but I think it may be smoother than the TBM?

I think the CF after the 5879 is the best solution I have found for smoothing the 5879 out while keeping it very touch sensitive and articulate.  Smoothing caps did NOT come close to smoothing it as much as this did, IMO. That 5879 tube seems to want to have some top end "hash" (Geezer's term) on it. Yet, I could not find a gritty or harsh OD tone at all with the CF after the 5879.

Ironically, with this CF after the 5879, I could not use any 12AT7 in the V2 position because it would have oscillations. I tried two different 12AT7. So I don't know if it's the "T7" current or bad tubes?  It works perfectly with no oscillation with 12AV7, 12AY7, 5751 (my current favorite) or 12AX7.

I took voltages and I'll post them later.  

I am wondering if the HoSo56 with the 5879 would sound good with the 5751 CF triode following the 5879 at the input?

Editable SCH versions are here:  http://www.el34world.com/Forum/index.php?topic=11455.msg106079#msg106079

With respect, Tubenit

[Geezer]

I REALLY like the idea behind this design.....working on putting this into my next amp, basically a HoSo front end, into this OD section (with some "bells & whistles" switching options).

Thanks, T!

G

[jojokeo]

tubenit - have you tried using a smaller/lower cathode resistor value on the CF triode after the 5979 yet? It should yield an even creamier and smoother gain response?

"the up-going cycles are very heavily compressed, but the down going ones are not, which generates a lot of second harmonic distortion. This is only made possible by the DC coupling, and is why this circuit is so often used in high gain amps- it can warm up a signal that already contains too many high-order harmonics, and return a rather fuzzy sound to a rich, creamy distortion tone. The effect can be increased by lowering the follower's cathode load resistor, to say, 68k, 56k or even 47k." <<---these values were suggested when the prior stage's CF load resistor is the typical 100k value.

[tubenit]

have you tried using a smaller/lower cathode resistor value on the CF triode after the 5879 yet? It should yield an even creamier and smoother gain response?

No, I haven't but I will when I get a chance and let you know if there is an improvement. Having said that, it's pretty smooth already.

With respect, Tubenit

[Fresh_Start]

May I ask a lazy question?

Are there any 9-pin tubes with a suitable pentode and triode in the same bottle?  I mean for the pentode/cathode follower topology.

As always, many thanks to tubenit for sharing his experiments.  If you'd just stop making progress toward "the best harmonics, sustain and bloom" plus "creamiest overdrive", I might actually pick up a soldering iron and build one of these darn things!

Cheers,

Chip

[tubenit]

I've wondered if the 6BM8 could be made to work?  In the ARCHIVES, I listed a one tube reverb using the 6BM8 pentode triode.   

With respect, Tubenit

[sluckey]

6AN8 and 7199 should have some possibilities. They were used a lot by Sunn and Ampeg.

[jojokeo]

6BL8 & 6AW8a too.

[tubenit]

Guys,

I am really liking the overdrive tones on this TOS 5879 with cathode follower. Very smooth, very clear overdrive with nice harmonics and sweetness to it.

If any of you try this, PLEASE post your results and what you think of it. This continues to impress me as a winning combination. I'd love to hear others trying this and getting similar results from it.

With respect, Tubenit

[jojokeo]

I've got some of those pentode/triode tubes w/ this exact intention but have been putting it off for a couple of builds now. But, it appears it may be getting moved up the list now? Have you thought of increasing the gain even more by splitting the load resistors? 

[tubenit]

Have you thought of increasing the gain even more by splitting the load resistors?

Honestly, I am really hesitant to change anything in the way of gain. And I don't need any more gain than this. There is more than an adequate amount here.

have you tried using a smaller/lower cathode resistor value on the CF triode after the 5979 yet? It should yield an even creamier and smoother gain response?

I may try a lower value cathode resistor to see what happens with that & if that actually adds more smoothness? Maybe change the 82k to a 68k or 56k and listen to that.

with respect, Tubenit

[William_G]

I agree with Tubenit !!

I built a TOS with reverb, it has vvr with super reverb trany and forty watt output trany. This is amp has Tubenit tone
stack mod as well. I really liked the clean channel, but the overdrive channel just did not sound as good to me. I did the smoothing cap change and that helped some. I have now changed to the cathode follower after the 5879 tube and
put the tone control after the OD level again. The clean channel,now without the depth control,sound as good or even a little better. The OD channel has the most improvement, any amount of overdrive from a little to alot has a very smooth sound to my ears. Thank you Tubenit for this lattest mod for the TOS amp, this a great amp!!!!!

William_G

[tubenit]

William G,

Hey thanks for posting your results and I'm glad the cathode follower worked out well for you also!

It really did smooth the OD section ALOT, IMO. I am very pleased with it.

With respect, Tubenit

[jojokeo]

I may try a lower value cathode resistor to see what happens with that & if that actually adds more smoothness? Maybe change the 82k to a 68k or 56k and listen to that.

I changed the CF like this from the standard 100k's in my amp that used the 6bm8 tubes to the first stage load resistor staying at 100k and the second stage cathode load resistor to 47k (half) and it did make the difference. Not by leaps and bounds but it was a nice change and I left it in. Thinking it might add a little more for you too to try?

[tubenit]

tubenit - have you tried using a smaller/lower cathode resistor value on the CF triode after the 5979 yet? It should yield an even creamier and smoother gain response?

"the up-going cycles are very heavily compressed, but the down going ones are not, which generates a lot of second harmonic distortion. This is only made possible by the DC coupling, and is why this circuit is so often used in high gain amps- it can warm up a signal that already contains too many high-order harmonics, and return a rather fuzzy sound to a rich, creamy distortion tone. The effect can be increased by lowering the follower's cathode load resistor, to say, 68k, 56k or even 47k." <<---these values were suggested when the prior stage's CF load resistor is the typical 100k value.

This works like you said it would.  There is a sweet spot though. If I went too low on the cathode follower resistor then it sounded thin. However, there was a very musical spot where it lost NO sustain but had a sweeter more musical tone to my ears and was possible more touch sensitive.

With respect, Tubenit

[jojokeo]

Thanks for the update! 

[Willabe]

There is a sweet spot though. If I went too low on the cathode follower resistor then it sounded thin. However, there was a very musical spot where it lost NO sustain but had a sweeter more musical tone to my ears and was possible more touch sensitive.[/quote]

Which was? 


          Brad         

[tubenit]

On this amp is was 65k so I used a 68k there.  The plate resistor is 82k.

with respect, Tubenit

[Willabe]

Thanks tubenit.

         Brad     

[Geezer]

I may try a lower value cathode resistor to see what happens with that & if that actually adds more smoothness? Maybe change the 82k to a 68k or 56k and listen to that.

I changed the CF like this from the standard 100k's in my amp that used the 6bm8 tubes to the first stage load resistor staying at 100k and the second stage cathode load resistor to 47k (half) and it did make the difference. Not by leaps and bounds but it was a nice change and I left it in. Thinking it might add a little more for you too to try?

OK, I tried the lower CF resistor on an amp with a "Hoso" type front end & it REALLY helped both the clean headroom of the "clean" channel AND the OD tone & smoothness! I hooked up a 100kL pot & basically tried every value from 100k to -0-.....I ended up on 39k for the CF cathode resistor ("normally" 100k on most standard CF designs). I lost some "power" with such a low value, but I have much more use of the gain pot now, with a wider sweep available. I can get the "lost power" back by just turning gain up up a bit higher.......

This was the final "touch" that this amp needed to be "perfect".

Thanks Guys!

G

[Tone Junkie]

It figures I built the TOS into TMB and now I want to play with the TOS again time to build. Thanks Bill

[jojokeo]

Hi Geezer,
I just checked my archives on the amp I did this on and it was inspired by your original mini-bassman w/ V1 paralleled. But then we changed to the 5879 and it became known as little wing. Then tubenit went and added VVR, reverb, and some tone stack mods which turned it into the 56T. There appears to be other derrivatives such as the 5879 blues amp, carolina blues rocket 5879, crazy vox 5879, and the hoso 56!  Am I leaving anything out? 
I guess you could add my version to it I called CherryBomb. With a few variations like running the 5879 w/ triode option - needed for cleaning things up a bit but also gives a great driving tone that's awesome which you can't get w/ too much harmonic content or distortion going early that the pentode gives at certain levels, the ltpi resistors changed to lessen the balance but yield a better sounding output, this cathode follower mod, switched bypass, etc...but nothing major really. I will say that the devil is in the details and tuning/voicing in the end that really pushes a promising filly into a glorified racing stallion. I hadn't played it for some time until last week going back and forth btwn Weber Blue and Celestion Gold alnico 10's. What a joy it still is and it's back in the rotation again. It's only drawback would be a need for more power but that's why I include preamp outs and poweramp ins when I can. :)

[Tone Junkie]

Anyway to sticky this to the TOS section so when I build it again I can find it.
Thanks Bill

[tubenit]

Actually, if I am remembering correctly ..................  here is the evolution of the TOS.

Geezer and I both built a cathode biased Dumblish HRM amp and neither of us were "wow'd" by it. It was just a real nice amp. That became the foundation for the TOS.

I think then that Geezer tried a 5879 in the first gain stage of the OD and didn't like it. However, I tried the 5879 in the second gain stage of the OD and liked it ALOT & that amp was the Carolina Overdrive Special (which was prior to the TOS).  The COS also had a one tube reverb which later got changed to an onboard effects loop.   The 5879 idea was obviously borrowed from Geezer's HoSo56 design.

Then Geezer changed the clean tone stack to a simple 5E3 tone stack and added the fatness paralleled triode and the Carolina Overdrive Special became the Tweed Overdrive Special.

Since then,  Geezer made the Tweed BluezMeister. I liked the clean channel on that so well that I changed my clean channel on the Tweed Overdrive to the Tweed BluezMeister which eliminated the paralleled triode "fatness". However, I just used a TBM one potentiometer version on the TOS. I have a gut feeling that the 5E3 tone stack could've been kept and would have gotten similar results by just changing the plate and cathode values to Geezer's TBM values  120k/3.3k  &  150k/1.8k.

After that I kept reading what you guys were saying about the cathode follower improving tone and decided to try that on the TOS. It worked! Much smoother tone.  I later added the "secret sauce" cap which seems to improve blooming and harmonics on both my amps.

Maybe Geezer can comment on what he remembers?

With respect, Tubenit

[jojokeo]

tubenit, I was trying to remember all of the original variations when we started using the 5879 before the Dumble HRM amp ideas which then lead to those you are talking of. I have a geezer schem of his mini-bassman dated back to '06. V1 was a paralleled triode then w/ 6BM8s. Then I've got the Little Wing with and w/out reverb schems that look to be dated at around Oct. of '09. They both have the same tubes at that time. I built my amp at that point also w/ the same tubes. I changed to the 5879 in Dec of '09. I have the HoSo56 dated 11/09 but saved the actual file as "revised 3/09 by degeezer". Now, what's wierd is I have your 56T schem w/ the 5879 dated 3/09. The Crazy Vox dated 12/09 and that's the first time I see the 5879 ran in V2 instead of V1. I know this is confusing and so am I even as I'm trying to figure out the evolution of using the 5879. You also were rebuilding your amp w/ various power tubes back then and I think ended up liking the 6aq5s correct?
Anyway, the Crazy Vox amp looks to be the first time I can see that documents you using the 5879 being cascaded into and I'm pretty sure this was all well before the Dumble amps and I don't show them until around 6/2010 - atleast mine's dated then and I thought we all started building/designing those about the same time? There were a lot of various versions and changes at that time for sure which makes things difficult to remember how they all came about. Big surprise there huh!? 
Here's the Crazy Vox schem I have. Maybe you remember it?

[tubenit]

The 5879 idea was obviously borrowed from Geezer's HoSo56 design.

Jojokeo,

I think your memory is fairly accurate & perhaps spot on?  It's kind of hard to keep track of some of the evolution of the experiments, but you've done a good job of tracking it with the use of the 5879 which was Geezer's introduction.

I tend to grab old schematics and just edit them into something new. Result of that is sometimes I forget to edit the date on the original schematic. Geezer does a MUCH more meticulous job keeping track of which version he is sharing and labels them more accurately than I do.  I'll try to do better in the future.

I had somewhat forgotten about that Crazy Vox or Crazy like a Fox scheme. (I think Geezer may have used both labels)


With respect, Tubenit

[jojokeo]

I think you were ahead of your own time on using the 5879 to be cascaded in to!? Ofcourse it's not exactly the same in a number of ways but the base idea is there. It took the HRM phase and almost a year later to refine it to it's current iteration which seems like you may have found a final desgin w/ this one? What do you think about this and has there been any current latest sound examples done?