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Bingo! Allen #75 paired up.

doucanoe

doucanoe

Registered Audio Abuser
I got home from work today and had a big heavy UPS delivery waiting for me. She is in need of a bath but if the traffic reports are accurate, needs a recap (dont they all) but tranny's all check out fine and dandy.

If everything is good to go, I have two ways to approach this.

1) recap and employ wiring mod to control excessive gain for 75w/ch of 6550 tube power

-or-

2) Same as above but also add the triode modification for 30w/ch triode.

Opinions?

RC
 

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Nice !

those are puuurdy

gives me incentive to get hopping on my Magnavox 150XX's :thmbsp:
 
Those are sweeeeet! If it was me (and I wish it was), I'd go with some really nice caps, and triode mode. Heck, whatever you do, those are gonna be top shelf.:thmbsp: Congrats, Jay
 
jaymanaa said:
Those are sweeeeet! If it was me (and I wish it was), I'd go with some really nice caps, and triode mode. Heck, whatever you do, those are gonna be top shelf.:thmbsp: Congrats, Jay
Click to expand...


I keep going back and forth between having all that tube power and sacrificing some of it for the sweetness Triode wiring would bring to the party.

Its very tempting to go balls to the wall and end up with a pair of tube mono's that would drive just about anything I could throw their way. On the other hand, 30 watt Triode wired mono's would be no slouch in the power dept. either.

With the speakers that you, Gary and myself among many others here are using, 30 watt Triode is almost overkill!

Gary keeps telling me to go for the power and he has a point. If I find that I really don't need the power, I could always do the Triode mod at a later time.

RC
 
Good point, I'm just a sucker for triodes. Most folks think the "sell-out" was transistors. I think it started with the pentode.:D (Just kidding, don't shoot Pak). I think there is something to lot's of spare power too though. When I started running KT90's in my Dynaco 70, it really opened it up, even on efficient speakers. Like you say, you can allways re-configure it after a while when you want to try something different. Jay
 
Very nice monoblocks. Like others have already expressed - I wish they were mine. Have you considered a toggle so you can switch between triode and pentode? That way you have the best of both worlds.
 
ldatlof said:
Very nice monoblocks. Like others have already expressed - I wish they were mine. Have you considered a toggle so you can switch between triode and pentode? That way you have the best of both worlds.
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Ahhh... no... Dang, that would be sweet. I have seen other amps that allow for that but had not thought about it for these. Im going to have to check into that. Thanks ldatlof!

RC
 
My amps are switchable,and they are rarely played in the triode mode. I just don't hear that much of a difference....
 
Powdercoat them. Hammered copper.

A haiku for you....

Heavy triode amp
How would you sound in Pentode?
Time to play again
 
Hey!!!,
It isn't as simple as strapping the finals into triodes if you want that configuration to work best. An OPTx load set for a pentode should take a whole host of things into consideration. Screen voltage and amount of NFB sharing the top spots IMO.

We could get into the idea of using a real triode instead of building one. It is a whole 'nother topic you may want to work out...:)

So here is the blanket statement:

There is a large difference between doing it, and doing it well.

For a given amp, it may be a step in the right direction to triode-strap. Rest assured that doing a good job on what amounts to a significant re-design can move the amp a lot farther. By connecting the g2 to the plate, you have resurrected Miller and the signal-based multiplication of the grid capacitance...not a good thing. How you deal with Miller is just part of the process.

Do it well, the rest of the amp certainly looks up to the task! Congrats on finding the second.
cheers,
Douglas
 
PakProtector said:
Hey!!!,

Do it well, the rest of the amp certainly looks up to the task! Congrats on finding the second.
cheers,
Douglas
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Thanks, I didn't think that I would locate another so quickly.

Holy cow! As usual Douglas, you have lost this technical neophyte after your first couple of sentences. Who the hell is Miller and what does he have to do with my amps?:D

Seriously, I think the point that you are trying to impress upon me is that finding a way to do something and finding the correct way to do something are two completly different animals. I am hearing you loud and clear on that.

Just to put your mind at ease, The amps will be going to a trusted tube amp tech. that Im sure will bring up the same concerns when I let him know what my plans are. I did get the schematic if your interested in seeing it.

One thing I want to avoid is significantly changing what these amps do best. If you have any thoughts on the excessive gain and the bypass mod. to solve it I would love to hear them.

RC
 

Attachments

Clmrt said:
Powdercoat them. Hammered copper.

A haiku for you....

Heavy triode amp
How would you sound in Pentode?
Time to play again
Click to expand...


You have hidden talent Colin. I like the powdercoat idea but Im too damn cheap. These might end up being the ugly duckling part of the system.

RC
 
Actually, I should keep things like that hidden.

Too damn cheap? I know what you mean.

I vote for the 30w versions. I mean, my cheapie little 8 watts (actually, I bought the marketing sheet on the SX-34, and they SWEAR it's a whole 11w) running through the EV's really shake the place.

You still run the Frazier/Altec/Fostex rig, right?
 
Hey!!!,
Miller is the gut who discovered the grid-to-plate capacitance of triodes gets multiplied by the amplification factor of the circuit. So instead of a 12AX7 having a few pF of input capacitance, it has more like 120 pF. For power triodes made from pentodes, it is the same thing, only g2-g1 capacitance is the quantity that gets multiplied and that is higher for a given plate dissipation than the g1-a capacitance of real triodes. Then the 6550 has a mu of more like 10 instead of ~4 for the 300B...:)

On getting rid of gain, eliminating the first triode gain stage would be my way. It is outside the global FB loop, and the amp is baisically a Mullard circuit; input pentode direct coupled to a twin triode LTP. It is a nice inexpensive and reliable circuit.

As you probably suspect, I'd be salvaging the Iron to try it in a slightly different way...not at all sure what you'll want to do...:) and by 'slightly' I mean completely different.
cheers,
Douglas
 
I wouldn't do the triode thing, I would leave them pentode. Iike the extra umph and like it better than the lesser power triode sound. Even with ultra efficient horn speakers I Listen to. I am sure Pak has a cure for both, but like he said, it would only have the iron of your existing amp, and use another output tube altogether. Remove the first stage as pak recomends, restore as is, and beef up the power supply a littl and see what you have, then mod/change from there.

Russellc
 
Thanks Pak and Russellc for your input. That helps quite a bit in understanding the Gain issue among other things. I spoke with my guy prior to him seeing the Allens or schematic. He also voiced his concern about changing anything within the GFB loop control gain so I think we are on the same track.



You would use the iron and redesign the rest eh? You are a dangerous man Pak, a very dangerous man:D I would love to hear (slightly dumbed down non-technical version) what you would do with the transformers as a starting point. Circuit, tubes, power output and why you would go that route.

Man, If I had half of the ability of some of you guys, I could really have some fun.

RC
 
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