Recommend Modern New Production 6550 for Mark III

Hello Everyone:

So searching the subject matter did not reveal anything recent like in the past 12 months. So I would like to get your opinion and recommendation on modern new production 6550 tubes for a older generation Mark III amp. My cousin is persuading his co-worker to sell to him his dad's amp. His father passed away some time but his co-worker never tested it. He did indicate there were no tubes except the small one (6AN8). So my cousin will do the typical maintenance but eventually will need to get new power and rectifier tubes. I have a couple spares of JJ 5AR4 to give him, but I have no idea which of the newer made 6550 is recommended for both sound quality and durability. Before anyone post to go with NOS or tested OS from a reliable vendor my cousin is on a tight budget so neither of those options will work at the moment. Besides, I recommended to him for testing he shouldn't use NOS or OS tubes. But he did make a point that he didn't want to go with the cheapest for testing and use better modern tubes when the amp is proven reliable. He wants one purchase to work for him under all situations.

Thank you

Take a look at Winged "C" 6550 tubes. Be sure to order in matched pairs or matched quartet.

Kevin

BNR_1 wrote:Hello Everyone:

So searching the subject matter did not reveal anything recent like in the past 12 months.  So I would like to get your opinion and recommendation on modern new production 6550 tubes for a older generation Mark III amp.  My cousin is persuading his co-worker to sell to him his dad's amp.  His father passed away some time but his co-worker never tested it.  He did indicate there were no tubes except the small one (6AN8).  So my cousin will do the typical maintenance but eventually will need to get new power and rectifier tubes.  I have a couple spares of JJ 5AR4 to give him, but I have no idea which of the newer made 6550 is recommended for both sound quality and durability.  Before anyone post to go with NOS or tested OS from a reliable vendor my cousin is on a tight budget so neither of those options will work at the moment.  Besides, I recommended to him for testing he shouldn't use NOS or OS tubes.  But he did make a point that he didn't want to go with the cheapest for testing and use better modern tubes when the amp is proven reliable.  He wants one purchase to work for him under all situations.

Thank you

A well matched pair of jj 6550 will do well. So will JJ kt-88 . jj 6550 is what i use
The key here is "well matched", this applies to all power tubes.

Not sure how you feel about using KT88s but Gold Lion seem to be one of the best new production tubes. You can get some tilted new stock, cosmetically challenged but electronically OK, for like $40 or so. I don't know enough to explain the difference between 6550s and KT88s, but for new stuff I hear the Gold Lions are quite good. I had a quartet in one of my amps and one went bad but we are not sure of the cause....could very well have been a failure in the bias circuit or weird spike, but I'm staying with them for now. My two cents...

I recall the higher quality of the Winged =C= tubes so I will add it to the list. But for some reason i thought they stop making tubes.

JJ and Gold Lions are duly noted.

Any others opinions and recommendations?

While it is some what related can the KT88 new production tubes be a simple drop in to the older version of the Mark III amps? I realize biasing is a must. I read in other forums that the KT88 can be used but it appeared that the Mark IIIs in the posting were the newer kits so I assume the PT is rated for such use. But for the older Mark IIIs can I use KT88s?

Thank you

Hi BNR --

the last version of the Dynaco Mark III's used KT88 power tubes with the A431 and P782Transformers, so the KT88's were a "drop-in replacement" for the 6550's after 1 or 2 resistors were changed.

There is an updated Mark III build manual on the Web (not the one posted on this Forum) that shows the Mark III's with Kt88's.

The link to the updated Mk3 Manual is:
http://www.the-planet.org/dynaco/Amplifier/Mark%20III.pdf

Any other questions, just ask.

Stew

BNR_1 wrote:I recall the higher quality of the Winged =C= tubes so I will add it to the list.  But for some reason i thought they stop making tubes.

JJ and Gold Lions are duly noted.

Any others opinions and recommendations?

While it is some what related can the KT88 new production tubes be a simple drop in to the older version of the Mark III amps?  I realize biasing is a must.  I read in other forums that the KT88 can be used but it appeared that the Mark IIIs in the posting were the newer kits so I assume the PT is rated for such use.  But for the older Mark IIIs can I use KT88s?

Thank you

As far as the MkIII amp, 6550 and KT-88 are equivalent.
When higher B+ is used KT-88 tolerates slightly more power.

On the more economical side I would recommend Valve Art KT88's from Antique Electronics. They run $122/matched quad. http://www.tubesandmore.com/products/T-KT88-VA

If you want truly matched tubes for sound quality and longevity then I recommend RAM tested tubes. They're more expensive but I would consider them a long term investment.
http://www.tubeaudiostore.com/powertubes.html

Thank you everyone.

Stew thanks for the link. I need to verify which amp my cousin has.

If the power tubes are KT88s but biased for 6550s do you think it would last longer? Sound quality maybe an issue, however. Don't know.

BNR_1 wrote:Thank you everyone.

Stew thanks for the link.  I need to verify which amp my cousin has.

If the power tubes are KT88s but biased for 6550s do you think it would last longer?  Sound quality maybe an issue, however.  Don't know.

Tubes are bias-ed the same, 1.4V ( 50mA ) on a dynaco, 0.5V ( 50mA ) on a tubes4hifi.

And bias should always be done when changing tubes since they all are dissimilar.

DynakitParts wrote:Take a look at Winged "C" 6550 tubes. Be sure to order in matched pairs or matched quartet.

Kevin

Hi Kevin,

You might not be aware that the SED 6550Cs are going for $300 to $400 per matched quad! A few guys with old priced stock left are just under $300 but the supply is apparently just about gone. We may have seen just about the last of these, in fact there are reports out now that "winged C/SED" tubes are no longer in production.

Its a sad day if that is true - and it likely is.

Hi Jim,
I didn't realize the current cost on these tubes...Wow!

It would be shame to see this brand go away much like the EI tubes some years ago. Appears that the
SED EL34 tubes are still priced reasonably....maybe it's a good time to stock up on a few quads. Do you have these in inventory?

Happy Thanksgiving!

Kevin

DynakitParts wrote:Hi Jim,
        I didn't realize the current cost on these tubes...Wow!

It would be shame to see this brand go away much like the EI tubes some years ago. Appears that the
SED EL34 tubes are still priced reasonably....maybe it's a good time to stock up on a few quads. Do you have these in inventory?

Happy Thanksgiving!

Kevin

Hi Kevin,

I have just a few single EL34s, I do have 10-20 6L6GCs (a quad or two), and about the same in 6550Cs. That's it I'm afraid. I'm not asking for the crazy prices you saw, but I don't have much left to offer.

On the EL34s, they are in the $180.00 - $200.00/quad range, and I find it hard not to recommend the KT-77 Genalex instead since the price is the same pretty much.

It is sad, very sad. Another long time tube maker calls it quits...

But a Happy Thanksgiving to you and yours - it will definitely brighten up the week!

So my cousin went with the JJ 6550 tubes. He also indicated the trannies are the P-782 & A-431 for output. I guess he could have gone the route of the KT88s.

Wow did not realize how pricey the Winged =C= has gone. Never thought the day would come when we feel compelled to hoard new (or recently new) tubes:D 

If anyone has further input or want to share their experience with modern-made tubes for the 6550 or KT88 please do so. I am always wanting more info and I'm sure there are others wanting the same.

Happy TG to all, and have a safe holidy.

Hi

I use a matched quad of JJ KT88 and in my opinion they sound really good. I like it in all their performance and specially the "solid state" low end.

IMHO very good quality price tubes.

Good listening with Dynaco.

Tiziano

If you look at the very last page of the manual linked by stewdan in post no. 6 of this thread. There is an addendum mentioning that if you want to use the kt88's then you should switch the 22K Ohm resistor with an 18k Ohm off the bias pot. This assumes you are going to use the original circuit board.

For what its worth, I just finished building a pair of new Dynakit's Mark III's, but I installed the Tubes4hifi's octal driver board. I ended up buying the JJ 6550 tubes for the output. On initial power up, I turned up the variac until I achieved a filament voltage of about 6.2 V or so and will run it there. With my line voltage often exceeding 125V that elevated the B+ higher than I would like for long tem reliability. For my project to hit the filament voltage of 6.2 V the variac was set about 118V. Good luck! Those are good sounding amps.

Elrick wrote:If you look at the very last page of the manual linked by stewdan in post no. 6 of this thread. There is an addendum mentioning that if you want to use the kt88's then you should switch the 22K Ohm resistor with an 18k Ohm off the bias pot. This assumes you are going to use the original circuit board.

For what its worth, I just finished building a pair of new Dynakit's Mark III's, but I installed the Tubes4hifi's octal driver board. I ended up buying the JJ 6550 tubes for the output.  On initial power up, I turned up the variac  until I achieved a filament voltage of about 6.2 V or so and will run it there. With my line voltage often exceeding 125V that elevated the B+ higher than I would like for long tem reliability.  For my project to hit the filament voltage of 6.2 V the variac was set about 118V. Good luck! Those are good sounding amps.

I have a ST70 and my outlet typically pumps out 123V. The bias could not be adjusted to lower the B+ at the target level and I was a bit lazy changing the circuit to lower the B+, so I ended up using a 5U4 rectifier. But eventually I am building a simple bucking transformer using a 6.3V filament transformer. This should achieve my goal of around 117V into the amp.

Good work on the bucking transformer. Just make sure can handle the power draw of those amps. I've thought of using a salvaged PS from some long dead radio and using the 12V filament windings to knock down the line level for some of my old radios, but those probably couldn't handle the current draw of two Mark III 's.   For me it's easier to just pick up a 10 Amp variac at a swap meet or EPay and run all my junk through it.  

Good luck, tonight I just noticed a beautiful deep blue glow at the tops and bottoms of the plates in the 6500's. Hope that's not a bad sign.

I just thought of something, considering how close the 6550's sit together on the Mark III wouldn't that put those fat boy KT88's too close.

The filament tranny I plan on using is rated for 10A. I believe those are more then suitable for my purpose. I don't own any Mark IIIs, but that will be my goal someday. Hopefully the bucking tranny will be capable of handling the 2 amps and then some.

I have no idea if the fatboy KT88s will be too close. I have seen images of EH KT88s on the Mark IIIs, and I just learned on my posting that the later Mark IIIs were designed around these tubes, but if the fatboys are much bigger than the average KT88s then someone will chime in.

BNR_1 wrote:The filament tranny I plan on using is rated for 10A.  I believe those are more then suitable for my purpose.  I don't own any Mark IIIs, but that will be my goal someday.  Hopefully the bucking tranny will be capable of handling the 2 amps and then some.

I have no idea if the fatboy KT88s will be too close.  I have seen images of EH KT88s on the Mark IIIs, and I just learned on my posting that the later Mark IIIs were designed around these tubes, but if the fatboys are much bigger than the average KT88s then someone will chime in.

KT-88 will fit fine in a Mk-III ( i once had a pair using genalex kt-88. I still have 2 of the used tubes to no purpose at all

Andy @ Vintage Tubes turned me on to a matched quad of Svetlanas awhile back for $100, but I think it was his last. I see there's a pair of Jim McShane-matched NOS General Electric 6550As quads on AudiogoN just now. $1800, but there's a lifetime supply if you like the GE sound.
https://app.audiogon.com/listings/tubes-general-ellectric-6550a-two-jim-mcshane-matched-octets-unused-2013-11-30-accessories-60085

I read great things about the GE 6550A. It is a balanced and clear sounding tube but it is the robustness that make it stand apart from other tubes of that era. But that price is a bit over my budget now and probably for the foreseeable future.

Those GE 6650's are for sale as two OCTETS at $1800. That's a bit over $100 a tube. Probably about 200 years worth of power tubes ;-)

Dave_in_Va wrote:Those GE 6650's are for sale as two OCTETS at $1800. That's a bit over $100 a tube. Probably about 200 years worth of power tubes ;-)

Yes, I misspoke. Heckuva lot cheaper than Tung Sols of 1960s vintage.

My favorite current production are the KT88EH by Electro Harmonix. I have tried the JJs, the Sovtek, and the Svetlana 6550 circle Cs and the EH sound best to my ears. I even tried the Sylvania 6550s which were my favorite back when they were still made and still like the EHs. Perhaps it is the KT88 sound that I prefer in my Mark IIIs.
Just my two cents.