pentode running as triodes/triode mode

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charliewired
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pentode running as triodes/triode mode

Post by charliewired »

I have read some articles about players who prefer the sound of pentode running as triodes/triode mode, appearantly you get a very warm compressed sound from this wiring idea. I just happened to buy some of Sarge's Poor Mans Single Ended deals - they sound fantastic as is {ultra high VOX'ey gain but extremely low vol} - but need lots of tampering in order to get em to run at peak volume and optimum efficiency. One of the things that made them so appealing to me was the fact that they have a separate 6V6 push pull section that was for lighting. Needless to say the Thoronson PTs pack alot of punch for this little unit - I was kinda wondering whether to set up the 6v6 section as triodes in a foot-switchable alternative. Before getting into all thaaaaaaaaat I kinda wanted to hear some sound samples of pentodes running in triode mode. Does anyone have any experience with this configuration and better yet can anyone suggest a website that has samples of this variety? or mabye upload some examples? I googled it but didnt have much luck.
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Broz
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Post by Broz »

Charliewired,
I also picked up one of these SE amps, but I think that either I am doing something wrong, or it's broke. I get some output, but at max vol I can barely hear it at all. That's not what you meant by extremely low volume is it? Sorry to be responding off the topic of your question.
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Re: pentode running as triodes/triode mode

Post by zaphod_phil »

charliewired wrote:...the sound of pentode running as triodes/triode mode, appearantly you get a very warm compressed sound from this wiring idea.
Most folks I've come across who have tried Triode mode said the opposite - ie the tone really sucks and you can get more hum. So I never bothered trying the idea after that.
Last edited by zaphod_phil on Thu 08/18/05 6:44 pm, edited 1 time in total.
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Post by rjgtr »

Well I wouldn't say the tone sucks at all. I own a couple of Rivera amps with Vintage/Modern (their term for Triode/Pentode) switches.

I personally prefer the more colorful sound of the Pentode mode most of the time. But the triode mode tends to be more compressed and is more pure. It is a great sound for Jazzy type stuff. I like it when recording becuase it offers another tone pallet.

It's very nice as an option.
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Post by charliewired »

rjgtr - you wouldnt have any recordings of that amp would you - Id love to hear it in that mode.
Broz - do you have the schematic that goes along with it - I posted it below - I will post some other ideas based offthis chassis later today.
heres some advice Tracy Norton sent me

CW
if you have one of those Moviola 1800's, here's a schematic I did of
that amp for reference. Lo output might be due to the fact that the 1/4
jack is a headphone out and speaker output is wired to that old cinch
jones 2 pin jack

take a look at the 1st pre stage
it's DC biased......rewire that gain stage to type 68k/1M to grid and
hack out the DC bias circuit

notice the B+ reduction resistor on the rotary sw (400 5W off of PT
secondary CT)

this amp gets loud thru a 2x12

hopefully this should help you Broz - posted below is the schem,
Charliewired
Last edited by charliewired on Fri 08/19/05 11:11 am, edited 1 time in total.
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Post by zaphod_phil »

rjgtr wrote: It is a great sound for Jazzy type stuff.
Ah, so it actually does suck! :lol:
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Post by rjgtr »

ZP,

:lol: :lol: :lol: Well I guess 'suck' is in the ear of the beholder! :lol: :lol: :lol:

It certainly isn't my choice for a rock or metal sound. It is just not punchy enough for that. If is definitely a softer sound.

Charliewired - Sorry I don't have any clips of that mode. Maybe head over to the Rivera amps website and see if they have posted any.
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Post by charliewired »

TTs wunderamp schem. appearantly this too had errors and im deleting it.
Broz just phone sarge or follow champ diagrams for guidelines.
Last edited by charliewired on Fri 08/19/05 5:13 pm, edited 2 times in total.
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Post by charliewired »

appearantly this was an outdated schem and I was told by the creator to just delete it lest someone mess up - my apologies
Charliewired
Broz just phone sarge or follow champ diagrams for guidelines.
Last edited by charliewired on Fri 08/19/05 5:14 pm, edited 3 times in total.
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Post by Broz »

CW,
Thanks for posting the Moviola schematic. I didn't have this, since the last time I e-mailed Terry, they were just trying to trace it out. So, is this the schematic of the original configuration or of the mods needed to make it go? I have connected my speaker to the wires to the 2 pin jack, and no joy on the volume. Does that rotary switch have to be in any particular position? I really don't follow the rewiring of the preamp. I assume the 1Meg from the B+ down onto the guitar jack is the DC bias that you mention. So I should get rid of this resistor, or use i to reference the input to ground? I don't even understand how the input signal makes it onto V1B with that 4 pin connector. Is that SW4 to allow you to bypass V1B and connect the input to V1-A (seems like a strange ordering of A and B). Anyway, thanks again. If you have anymore info or hints on this thing I would deeply appreciate it.
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Post by charliewired »

Yes the shunt switch needs to be one way or the other {the one beside the tone switch on the side of the chassis}- its one way on one of the chassis' I have, and the other on the second one!{I havent checked out the other 4 yet as some are in the mail still LOL} There will be no sound unless the shunt is set correctly. I havent actually examined the schem side by side with the unit yet, mine are low vol but soundng good >although I had to bypass an on/off switch to get one of em working. No doubt the caps on these are in various states of crappedoutness- I suggest going over them {after thoroughly discharging them of course} with your Multimeter and seeing how f**ked they really are - I mean replacing those is job one anyway, seeing as how old they are.
I expect your unit will sound good as well, as soon as you work out a bug or 2. Like I said I have designs based on the Champ, and thats the way Im going to go with mine, there are 4 stage preamp designs listed in a couple of sketches so its easy to design these little guys after the schem by rote. not sure how its gonna work out with the OT we'll have to see. Like I said if you want these diagrams email me. Other than that be careful cutting out the lighting sections as the voltages really jump -also call Sarge {email him and get his # if you dont have it} I have been in constant phone contact with him and he is as helpful as he can possibly be.
Im taking my sweet time with these as my cap order hasnt arrived yet and Im running the old ones, you''ll get it dialed and when you do Im betting you'll be impressed with these little suckers too.
Cheers
Charliewired
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Post by aphekgreg »

Back to the Pentode/Triode switch, can you do the same thing with EL84s? If it doesn't do any damage, I can't see a reason not to add it to every amp. Even a Deluxe or Champ can be too loud sometimes.

I don't know how it sounds on small amps, but I like it on EL34 Marshalls. I had a Silver Jubilee head with it and I prefered it on the half power setting. I've just built a 50 watt Plexi head and like it better on that too. It has a softer, slightly grittier sound. Not the sound for high gain sounds, but more like a Marshall crossed with a Tweed Fender.

I'm going to add a switch to my '64 Bassman too. Don't worry, I'll be using the ground polarity switch hole.

So, are there tubes or circuits that you shouldn't try this with?
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Post by DutchMarco »

aphekgreg, it also works with EL84s. You connect g2 to a, instead of to it's own supply. this noticeably reduces power, whilst maintaining most of the tone. Though it's not a good rock tone, it will work for mellower types of music. But it is very much compressed, the sound literally feels flattened. It's not as lively as it is on pentode (or tetrode) mode.

I wonder what it would be like on preamp pentodes...
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Post by zaphod_phil »

DutchMarco wrote:You connect g2 to a, instead of to it's own supply.
Not directly - you should have something like a 100 ohm or 470 ohm between each tube's Anode and it's Screen grid, to help prevent the screens getting fried. I therefore recommend Jason's Screen/PSU mod, as implimented in the Lite IIb design for when you're running in pentode mode, as that will make it easier to switch between the two modes.
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Post by aphekgreg »

Thanks guys, I'll give that a try. When I first looked at the Silver Jubilee schematic, it just looked too simple. I checked some different schematics to make sure. Definitely works well with EL34s. I don't hold much hope of it sounding great with EL84s, but we'll see.
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Post by aphekgreg »

Thanks guys, I'll give that a try. When I first looked at the Silver Jubilee schematic, it just looked too simple. I checked some different schematics to make sure. Definitely works well with EL34s. I don't hold much hope of it sounding great with EL84s, but we'll see.
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Re: pentode running as triodes/triode mode

Post by Beatwolf »

Would love to get a copy of the Moviola 1800 schematic. haven't really modded mine yet but it's full of mids. hardly any lows and highs.
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