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View Full Version : Tubes to AVOID in cathode follower position of amps


markflo
03-25-2010, 11:52 PM
so i've been reading up on some threads and forums about tung sols and sovtek lps being not good for plexi style amps or amps with cathode followers on them. any other tubes we should avoid placing in this position?

Blue Strat
03-26-2010, 05:42 AM
Those are the only 2 I know of.

Roe
03-26-2010, 06:31 AM
ditto

donnyjaguar
03-26-2010, 09:04 AM
Is this an issue with the voltage differential between the filament and cathode? My thinking is a CF imparts next to nothing on the signal because it has no voltage gain.

Blue Strat
03-26-2010, 09:14 AM
Is this an issue with the voltage differential between the filament and cathode?

That's the general consensus. This is the only type of circuit where the cathode "sees" 100 volts or so.

Ronsonic
03-26-2010, 10:48 AM
Back in the dark and dim past, there were spec sheets provided by each manufacturer for the tubes they produced. These had specs for things like cathode/heater voltage. Nowadays, no spec sheet, no spec. Makes manufacturing so much easier to not have a bogie value to shoot for.

conundrum
03-26-2010, 10:50 AM
My thinking is a CF imparts next to nothing on the signal because it has no voltage gain.

Cathode followers have unique overdrive characteristics even though they have less than unity gain.

Blue Strat
03-26-2010, 11:17 AM
Back in the dark and dim past, there were spec sheets provided by each manufacturer for the tubes they produced. These had specs for things like cathode/heater voltage. Nowadays, no spec sheet, no spec. Makes manufacturing so much easier to not have a bogie value to shoot for.


Funny about that, eh?

My favorite is when new manufacturers release a "high grade" version of a standard guitar amp tube (say, a 7025) that doesn't meet the spec of the standard grade item (12AX7). ;)

Roe
03-26-2010, 04:01 PM
in the early marshall 100watter, the cathode sees more than 200v

markflo
03-26-2010, 07:29 PM
so to all you guys with cathode uhm...amps...what do you guys use? right now i have an ehx 12ax7 in there. is that ok?

TweeDLX
03-26-2010, 11:24 PM
I used those in my JTM 45 build. Worked OK... no issues.

WaltC
03-27-2010, 12:22 AM
in contrast to a lot of folks, I've had good luck w/ the JJ ECC-83's, both in V1 situations and in cathode follower roles. Not as good sounding as the tung sol re-issues, but not as failure prone either.... I really need to start buying my tung sol's from Mike K <G>...

59Vampire
03-27-2010, 11:58 PM
i have a marshall tmb 18 watt clone.. i like to switch between delta hollands and beleive it or not a tungsram or a telefunken. currently im running a brimmar cv4004 with good results

Mickey_C
03-29-2010, 08:00 AM
Do you have any links (other than this thread) that discuss the issues with this tube for a CF? I've been using them for sometime without a problem, so I'd like to understand what the issue is.

I am also wondering if this is a recent problem - as I've been shipping amps with these since they first came available. I do an 8 hour tube burn in with new amps, and any tubes that make it through that last longer than I know about.

hasserl
03-29-2010, 08:20 AM
It's been some time ago now, but I had 2 Tung Sols fail in a very short period of time in a CF application, one right after the other. I stopped using them there after I lost the 2nd one.

RockStarNick
03-29-2010, 09:13 AM
This is a dumb question, but how does one know if your amp has a cathode follower in V2 or not?

bonertone
03-29-2010, 09:47 AM
We had some terrible issues with the 12AX7EH but only in certain positions...cathode follower positions being one of the most common points of issue.

The problem is either right away or....worse.... everything seems fine then 30 or 40 hours of service then they start to pop or crackle.... most common an annoying background hum that grows in intensity over time.

I ended up sending several hundred 12AX7EH back.

We swapped them for TS RI and Mullard RI ...had the same issues with the Tungsol RI but for some reason the Mullard RI is better...still have had a few problems with noise but nothing like the EH or the TS RI.

The tube from New sensor that seems to survive that position is the Sovtek 12AX7WA. also the chinese 12AX7's seem to work as well...neither being my first choice.


Out of frustration I emailed New Sensor for an explanation and this is what I got:

Spiral filament tubes do not work well in cathode follower circuits and are prone to failure. This appears to be due to the closer spacing of the spiral filament to the cathode. Spiral filament tubes include the 12AX7LPS, 12AX7EH, Tung-Sol 12AX7, Mullard 12AX7 reissue, and JJ ECC83s/12AX7. For cathode followers and phase inverters, I have had good luck with Sovtek 12AX7WA/WB/WC series tubes.

ripoffriffs
03-29-2010, 02:04 PM
Here's my experience from yesterday.....

I was trying out a different pair of EL-34s in a JCM800/1987 (4-input non-master). I also decided to replace V1 with Tung-sol RI's. This is before I even read this thread. I was biasing using the Weber Bias Rite. I finished and plugged a guitar in just to see how it sounds while bias rite was still attached.

After 30 seconds of playing, volume began dropping steadily. As if the standby was switched. I look at the bias rite and plate voltage and idle current is still there unchanged.

Turned it off and let it cool. Replaced the Tung-Sol with the stock tube. Works perfectly as if nothing happened. Meanwhile Tung-Sol is dead.

bluesy
03-29-2010, 07:41 PM
This is a dumb question, but how does one know if your amp has a cathode follower in V2 or not?

.....how does one know?

Jack Dotson
03-29-2010, 09:24 PM
.....how does one know?

Add me to the list; I'd like to know as well. I don't know if my Lucky 7 has the CF or not, but the issues described sound like what I've experienced as well.

My amp came with a 5751 in V1 and a JJ in V2. Noisy, but worked and sounded pretty good. As always, I can't resist trying different tubes and rolled in a set of TS's and got nothing but hiss and hum. Tried the TS's again, but this time using only one at a time with the JJ, but the result was that same. The JJ is noisy too, but usable. I decided to try a couple of cheaper tubes that I keep for spares, a Sovtek and a Ruby and the amp likes both of these regardless of the position their used in.

Funny thing is that once I rolled the 5751 back into V1 it died. I've got the Ruby in V1 now and JJ in V2, a little hiss, but not too bad (seems to be a characteristic of the amp) and practically no hum.

Maybe just a bad batch of tubes or do I have a CF in my amp? Anyone know?

Tks.

Blue Strat
03-29-2010, 09:32 PM
.....how does one know?


You'd have to either have a schematic and be able to ID a cathode follower circuit on it, or ask someone who knows. Those are the only options.

Asking the amp builder is certainly a foolproof way to find out.

Maybe we can compile a list of amps and socket numbers.

Blue Strat
03-29-2010, 09:33 PM
Add me to the list; I'd like to know as well. I don't know if my Lucky 7 has the CF or not, but the issues described sound like what I've experienced as well.

My amp came with a 5751 in V1 and a JJ in V2. Noisy, but worked and sounded pretty good. As always, I can't resist trying different tubes and rolled in a set of TS's and got nothing but hiss and hum. Tried the TS's again, but this time using only one at a time with the JJ, but the result was that same. The JJ is noisy too, but usable. I decided to try a couple of cheaper tubes that I keep for spares, a Sovtek and a Ruby and the amp likes both of these regardless of the position their used in.

Funny thing is that once I rolled the 5751 back into V1 it died. I've got the Ruby in V1 now and JJ in V2, a little hiss, but not too bad (seems to be a characteristic of the amp) and practically no hum.

Maybe just a bad batch of tubes or do I have a CF in my amp? Anyone know?

Tks.


What amp (or did I miss it)?

markflo
03-29-2010, 09:56 PM
Perhaps he was referring to the Fuchs Lucky 7 amp?

OT question to the tube kings... How do the matsushitas and BELs sound compared to the real mullards?

Jack Dotson
03-29-2010, 11:09 PM
What amp (or did I miss it)?

Lucky 7.

Wayne Alexander
03-29-2010, 11:26 PM
The only one I know of is the current reissue Tung-Sol 12ax7. That's not to say there aren't others but tube experts have told me that tube can't hold up to a cathode follower position.

Blue Strat
03-30-2010, 05:58 AM
Perhaps he was referring to the Fuchs Lucky 7 amp?


DOH! A quick email to Andy Fuchs will reveal the answer.


OT question to the tube kings... How do the matsushitas and BELs sound compared to the real mullards?


There's absolutely no consensus on what sounds better than anything else (trust me, 12 years talking tone with tone fiends).

You've got to hear it for yourself.

markflo
03-30-2010, 09:12 AM
Cr@p. Now i gotta get me som matsushitas and some BELs! I'm not really asking which one's better. More of its charachteristics. How are its highs, mids, and lows compared to its british & dutch cousins?

Blue Strat
03-30-2010, 09:34 AM
Cr@p. Now i gotta get me som matsushitas and some BELs! I'm not really asking which one's better. More of its charachteristics. How are its highs, mids, and lows compared to its british & dutch cousins?

You'll still have to hear them for yourself. It's like asking the difference between orange and amber...and one person in the conversation is mildly color blind. ;)

Mickey_C
03-30-2010, 11:25 AM
Out of frustration I emailed New Sensor for an explanation and this is what I got:

Spiral filament tubes do not work well in cathode follower circuits and are prone to failure. This appears to be due to the closer spacing of the spiral filament to the cathode. Spiral filament tubes include the 12AX7LPS, 12AX7EH, Tung-Sol 12AX7, Mullard 12AX7 reissue, and JJ ECC83s/12AX7. For cathode followers and phase inverters, I have had good luck with Sovtek 12AX7WA/WB/WC series tubes.

That's what I was looking for -- thanks.

Interesting that I loved the tone of the Mullard RI tubes, but found them to die prematurely. I haven't seen the Tung Sol have an issue but maybe I have had especially good luck. FWIW - the filaments in my amps are 12.6VDC - not sure how that would bear on the issue.

Regardless, I'll be looking at substitutes as well -- great information, and thanks to Jeff for pointing me this way.

Mickey

bonertone
03-30-2010, 11:47 AM
Good to know about the 12.6vdc... that could be a solution.

I know New Sensor suggests a dc filament on the 12AX7"LP" model

I've also noticed less incident on the lower plate voltage stuff.

Fuchsaudio
03-30-2010, 02:07 PM
Lucky 7.

There is no cathode follower in a Lucky-7.

AS far as CF tubes, the Ruby's hold up, I'm sure others do too. Avoid the Russian Tung-Sol/Eh/Sovtek and their variants, which die prematurely.

It's a tube issue, pure and simple, not a circuit issue, or an amp manufacturer issue, it's the tubes silly.

The RCA manual says 200 volts heater to cathode is spec, and the Russian tubes fall way short of handling that, period.

Our loop has 30 volt cathode voltage, and we still saw Russian tubes croaking...

markflo
03-30-2010, 04:39 PM
Do the tubes you put in the CF affect the feel or sound of the amp? I'm deciding whether i should get a NOS just for it or get a chinese one (i mostly have ts and eh)

Blue Strat
03-30-2010, 08:31 PM
Do the tubes you put in the CF affect the feel or sound of the amp? I'm deciding whether i should get a NOS just for it or get a chinese one (i mostly have ts and eh)

Every socket will have some effect on tone...all the signal has to go through the CF, nothing bypasses it, so it HAS to have an effect.

markflo
03-31-2010, 01:16 AM
you da man mike! thank you for the info!

Fuchsaudio
03-31-2010, 10:42 AM
Every socket will have some effect on tone...all the signal has to go through the CF, nothing bypasses it, so it HAS to have an effect.

I will "half agree" with Mike....lol. :nuts

The cathode follower position (s) are the least likely area to affect tone, imho. Gain positions (non cathode follower positions) tend to be the most revealing of a tube's sound and shortcomings. A cathode follower operates at 100% feedback, is therefore theoretically 0 gain (actually a half db or so less), so it shows tonal differences and microphonics less than other spots..

tommytomcat
03-31-2010, 11:42 AM
I'm glad I ran across this thread and CRAP, I just tried Tung Sol RI's in v2 & V3 of my 5E7.. Sounded great, but too much gain. Put a JJ 12AT7 in V3 (the PI) and the gain was close to where I like it. There was more definition with the TS RI in V2. Oh well...

hasserl
03-31-2010, 02:40 PM
I will "half agree" with Mike....lol. :nuts

The cathode follower position (s) are the least likely area to affect tone, imho. Gain positions (non cathode follower positions) tend to be the most revealing of a tube's sound and shortcomings. A cathode follower operates at 100% feedback, is therefore theoretically 0 gain (actually a half db or so less), so it shows tonal differences and microphonics less than other spots..

However, only 1 of the 2 triodes in a typical 9 pin preamp tube is used the cathode follower, the other triode is typically used for a gain stage, where it will have more of an effect on the tone, imho.

Mickey_C
04-03-2010, 11:55 AM
However, only 1 of the 2 triodes in a typical 9 pin preamp tube is used the cathode follower, the other triode is typically used for a gain stage, where it will have more of an effect on the tone, imho.

What he said.

And marshall style preamps do exactly that -- one triode is the second gain stage of the amp, and the other is a cathode follower used to drive the tone stack. And it's ironic because the CF existence in the marshall is an artifact of Leo's experimentation with different bassman circuits - it's not really necessary at all with the existing tone stack - and jim and ken just copied it. If you are power scaling a preamp design, it's a whole other can of worms too, as cathode followers do not scale well.

And now I guess we should add this new issue to the list of reasons why not to put a CF in a modern design - sounds like Russian tube makers don't read the original spec sheets, and we will probably see this problem more too.

Thanks for all the info guys - and thanks to mike at KCA NOS for being ahead of the ball!

Fuchsaudio
04-03-2010, 01:19 PM
While I agree on "the gain stage in same envelope" concept, I disagree on the stack. If you model or listen to the stack with and without the follower it certainly behaves and sounds different. The whole premise of how a stack works, is based on the source impedance and component values in it....:stir

markflo
04-03-2010, 03:59 PM
If chinese tubes are good with Andy they're good with me! Fantastic sounding amps those Fuchs. I just don't wanna "waste" nos tubes on a socket which will hardly make a difference tonewise

midnightlaundry
03-16-2014, 09:31 AM
Back FTD

insanecopilot
03-16-2014, 09:23 PM
I built a AX84 high octane awhile back, and this uses a cathode follower. It does add a Kind of an edge to the distortion which i like. So i think the cathode follower is a useful circuit.
I use a long plate JJ ecc803s in the v2 position and tung sol v1. Three years now with no problems.

hdahs143
03-17-2014, 09:14 AM
I think New Sensors response about "spiral filaments" is a smoke screen. Simply because they are the manufacturer of all of the problem Russian tubes.

The JJ is a spiral filament tube and works fine in a CF spot, as do the Ruby Chinese. As a matter of fact when Boogie put out their advisory on this, they switched to JJ as their stock preamp tube.

Fuchsaudio
03-17-2014, 09:55 AM
Spiral-shmyral...lol

The RCA manual calls for a 200 V peak heater/cathode voltage differential. In a typical Fender PI or the Bassman/Marshall tone stack driver the voltages can be approaching that in some cases. It's about not meeting specs, not spiral filaments....that's complete bs. especially when it seems you make every tube that's failing.