My first thought is that the primary impedance is too high for four 6550 tubes.
Two 6550 tubes work best with 4200 Ω, but 5,000 Ω is not that far off.
You might want to look at KT120s as a possible alternative. Two of those will give more power than the 6550 and you could get over 100 Watts RMS with just a pair.
It would be better if that transformer was a little lower impedance, but others here should be able to advise you on what to do next.
Not a fan of that topology. I don't like using intermediate transformers as they are just one more component that can add distortion, but done right it can be okay.
There are better topologies out there.
^4D32, a pair will give you 120 watts, class ab2
http://frank.pocnet.net/sheets/138/4/4D22.pdf
http://frank.pocnet.net/sheets/138/4/4D22.pdf
Seems to me I've seen those xfmr datasheets and schematics posted before. Maybe one of Wrenchone's threads? You might want to confirm the primary Z, as I seem to recall some comment about it being higher than the 5K spec. (put 120V across the full primary and measure the Vac on the 8 Ohm secondary) (The 5K figure does calculate out about right though for a 700 V B+ shown in the 2nd schematic. 320Wpeak = 632V x 632V/1250)
If it is too high a Zpri, then you could use two OTs: primaries in parallel and secondaries in series. That would reduce the primary Z by 1/2. And would either double the watt rating at 40 Hz or lower the low freq. spec to 20 Hz at the same Watts. Uh, wait a second, I think that may lower the effective primary Z by 1/4. Maybe can use the lower Z secondary taps to series together for an effective 1/2 Zpri.
Or just use a 4 Ohm speaker load on the 8 Ohm tap of one OT.
If it is too high a Zpri, then you could use two OTs: primaries in parallel and secondaries in series. That would reduce the primary Z by 1/2. And would either double the watt rating at 40 Hz or lower the low freq. spec to 20 Hz at the same Watts. Uh, wait a second, I think that may lower the effective primary Z by 1/4. Maybe can use the lower Z secondary taps to series together for an effective 1/2 Zpri.
Or just use a 4 Ohm speaker load on the 8 Ohm tap of one OT.
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I want to run Groove Tubes 6550R tubes as I have a bunch of new ones to work with, And these OPT were made for this tube.
He is what they say about them
The Groove Tubes GT-6550R is the highest power pentode tube available for Hiwatt, THD, Ampeg, Marshall and GT amps (as well as other amplifiers). The "R" version is easier to make distort or distorts at a lesser volume than does the 6550A (also called "softer"). It requires more gain to the tube to distort than the 6550C tube. This tube as well as the 6550C is great for tube Hi-Fi amplifiers because of the more gain with less distortion.
The "Hardness" value shows the amount of gain before distortion. So a hardness of "1" will distort much sooner than a value of "10". I ended up putting a 6550R in my THD univalve amp. I love the "woody" sound it provides. It's the same type of tube used in some Marshall amps in America back in the 1970's. It takes more gain to get it to distort so if you want a more normal distortion range get a 2 or 3 hardness, if you want more gain then get a 4 or 5 hardness. If you want a loud powerful sound say for a bass guitar (Ampeg SVT) then get a 7 or 8 hardness.
When cranked I get more of a midrange "wood" tone but the tube is known for it's brash odd harmonic sound in class A/B amps (the THD univalve is Class A). It favored by heavy metal guitarists that like to play loud. It sound best for metal when the preamp stages are melting
Features
He is what they say about them
The Groove Tubes GT-6550R is the highest power pentode tube available for Hiwatt, THD, Ampeg, Marshall and GT amps (as well as other amplifiers). The "R" version is easier to make distort or distorts at a lesser volume than does the 6550A (also called "softer"). It requires more gain to the tube to distort than the 6550C tube. This tube as well as the 6550C is great for tube Hi-Fi amplifiers because of the more gain with less distortion.
The "Hardness" value shows the amount of gain before distortion. So a hardness of "1" will distort much sooner than a value of "10". I ended up putting a 6550R in my THD univalve amp. I love the "woody" sound it provides. It's the same type of tube used in some Marshall amps in America back in the 1970's. It takes more gain to get it to distort so if you want a more normal distortion range get a 2 or 3 hardness, if you want more gain then get a 4 or 5 hardness. If you want a loud powerful sound say for a bass guitar (Ampeg SVT) then get a 7 or 8 hardness.
When cranked I get more of a midrange "wood" tone but the tube is known for it's brash odd harmonic sound in class A/B amps (the THD univalve is Class A). It favored by heavy metal guitarists that like to play loud. It sound best for metal when the preamp stages are melting
Features
- Great Crisp tone
- Nice break up
- High power
- Solid, tight bass
- Excellent value
I want to run Groove Tubes 6550R tubes as I have a bunch of new ones to work with, And these OPT were made for this tube.
He is what they say about them
The Groove Tubes GT-6550R is the highest power pentode tube available for Hiwatt, THD, Ampeg, Marshall and GT amps (as well as other amplifiers). The "R" version is easier to make distort or distorts at a lesser volume than does the 6550A (also called "softer"). It requires more gain to the tube to distort than the 6550C tube. This tube as well as the 6550C is great for tube Hi-Fi amplifiers because of the more gain with less distortion.
The "Hardness" value shows the amount of gain before distortion. So a hardness of "1" will distort much sooner than a value of "10". I ended up putting a 6550R in my THD univalve amp. I love the "woody" sound it provides. It's the same type of tube used in some Marshall amps in America back in the 1970's. It takes more gain to get it to distort so if you want a more normal distortion range get a 2 or 3 hardness, if you want more gain then get a 4 or 5 hardness. If you want a loud powerful sound say for a bass guitar (Ampeg SVT) then get a 7 or 8 hardness.
When cranked I get more of a midrange "wood" tone but the tube is known for it's brash odd harmonic sound in class A/B amps (the THD univalve is Class A). It favored by heavy metal guitarists that like to play loud. It sound best for metal when the preamp stages are melting
Features
- Great Crisp tone
- Nice break up
- High power
- Solid, tight bass
- Excellent value
What are you building, a guitar amp?
Everything you have suggested as far as components, including the tubes, were spec'ed for guitar amps, not HiFi.
If you want a big guitar amp you are off to a good start. If it is a HiFi, then I think you will soon find that it will not meet your desires and you will be starting over again.
If I were you I would restart my project by writing down all the requirements (design goals) and then reviewing those with the gang here. Be prepared to explain why for all of your requirements. You are just trying to define what to build.
Once the requirements are done we can move into the how to build phase.
Well the OPT are not what they appear. They will run the full 20-20,000hrz range. The test in the paperwork was just the THD test and was ran between 40-15,000Hrz So These will be just fine for Hi-Fi.
It says right in the description above
" This tube as well as the 6550C is great for tube Hi-Fi amplifiers because of the more gain with less distortion"
So the tubes will work also?
Now the PT he is sending me were made to run these OPT at 160w 4x 6550
I seem to have the parts needed to start, Now a design to go off of would be my next step?
WO
It says right in the description above
" This tube as well as the 6550C is great for tube Hi-Fi amplifiers because of the more gain with less distortion"
So the tubes will work also?
Now the PT he is sending me were made to run these OPT at 160w 4x 6550
I seem to have the parts needed to start, Now a design to go off of would be my next step?
WO
I like this idea? This seems to be a good way to go and I read some bad reviews on the tubes I have so I may need to rethink the 6550 thing.
WO
WO
Because you appear to be approaching the project all wrong.
I don't believe that I am alone in that feeling because there are some very good contributors on this forum that simply have not decided to get involved because, simply put, they have seen this before.
I understand where you are coming from and your desires, but I have also spent a 25 years in electrical engineering and I know a few things about best practices.
My discouragement, and I am sure the same is true for others, is that you already appear to have your mind made up, your goals are not aligned with your needs, and you do not recognize the value in the opinions and experience of others on the forum.
I am not saying this to be unkind or mean, but sincerely trying to help you get the most out of the journey you are trying to start.
Anyway, that is my opinion and it is strictly based on my feelings and the only reason I keep responding is because I would really like you to succeed and build something both educational and useful. The former is usually no problem to accomplish, but the latter can often be very ellusive.
The ideal impedance for two 6550s is 4,200 Ω. Four 6550s would be half that value or 2,100 Ω. That is a far cry from 5,000 Ω.
These transformers are also not Ultralinear (they lack the screen taps).
I just looked up the KT88 data sheet and I did find that two KT88s in tetrode mode with a cathode bias have an impedance of 9,000 Ω. In this mode four tubes would match pretty well with your transformer.
Maybe someone can enlighten me on whether this is a viable option.
What other tubes could be used with this Transformer? I am open to any sugestions? I am not trying to build something that will not meet my needs. I am just going off of a man that has been working on tube amps for ever. And has a very well known name in the field! I am not saying he is not wrong but why would he steer me in this direction? He does not need my $$$
WO
WO
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What about this tube?
KT120
[FONT=arial, helvetica]New Sensor now announces the Tung-Sol KT120, which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family. A pair of these tubes in push-pull configuration can deliver power levels of 150 or more watts. When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life. However, taking advantage of the higher current handling capacity of these tubes, a very unique and super powerful and stable amp can be designed using the Tung-Sol KT-120.
As of November 2010, Audio Research Corp. is using the Tungsol KT120 tube exclusively in all new power amps.[/FONT]
KT120
[FONT=arial, helvetica]New Sensor now announces the Tung-Sol KT120, which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family. A pair of these tubes in push-pull configuration can deliver power levels of 150 or more watts. When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life. However, taking advantage of the higher current handling capacity of these tubes, a very unique and super powerful and stable amp can be designed using the Tung-Sol KT-120.
As of November 2010, Audio Research Corp. is using the Tungsol KT120 tube exclusively in all new power amps.[/FONT]
There are simpler circuits around i.e Tubelabs....I would be cautious about sales talk when claims are made with newly designed tubes boasting sportlich prowess. The best cars can breakdown under stress test and my experience with recently made New Sensor 6550s' is it hasn't time proven reliability. So I'm avoiding this type. OMO.The problem for constructors is tube longevity, when todays vendors have brought down the reliability hours by more than 2/3, so 3000hrs or so may be finito, compared to 10,000 hrs back in 1960. Modern day tubes run in older circuits may find the going too hard. Vacuum and materials aren't what they used to be.
The original GE A version is very hard to find now, was the best hard working tube ever made.
BTW, KT88 circuits never use a 9K A-A o/p tranny....4-5K A-A is the norm.
richy
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Yes, they can run from 20 to 20khz, but at what wattage? I have a Peerless transformer that was made for a 260 watt amp that will do 20-20khz at under 10 watts, but at power (260 watts) it won't do near that. At 260W it would be lucky to get 40-15khz. And this transformer I have weighs around 70 pounds so it's limited bandwidth has nothing to do with its size.
Ask your guy at what power will your OPT do 20-20khz. I guarantee you that it will not be at 200 watts.
Well the specification document for that transformer states 160 Watts right in the drawing title and the specification is listed as 40 Hz to 15 kHz ±2 dB.
What is disturbing is the transformer is not even a ultralinear winding, so you loose the advantage of the UL taps and lower distortion.
To answer Wild One's question of why would his supplier sell him something that is not quality... Well, I am not questioning the quality, but the applicability of the transformers.
As an example, you can buy the finest delivery truck in the world, but it will be an absolute failure at the race track, Conversely, a race car is rather useless for delivering packages for UPS.
Assuming that the transformers are made from excellent stock, they appear to be constructed for guitar amps, which have a completely different criteria than a HiFi amp, just like the stock of 6550s you have.
Additionally, you do not want a HiFi amp with any distortion or frequency limitations. Distortion in a guitar amp is desirable. Distortion in a a stereo amp is not.
The recording studio already has the distortion mixed in. The last thing you want to do is add more distortion and add it to elements of the sound (i.e., other instruments, voice, etc.) that were not there in the beginning.
Actually, chances are, he will probably not even be using it up to 10W powers with his current setup of uber efficient horns.
, unless he desires to blow his roof off and deafen the dogs in his neighbourhood (not to mention his neighbours too). So perhaps these transformers will serve him well, but perhaps not to 200W levels. Just a little rant here, I do not understand his need for such a "powerful" system. Maybe because he can? But he seems a little misdirected with his choices. Most of his parts choices are based on "commercial blurb", rather than tried and tested designs. Those who have designed and worked with such high power designs have offered their views regarding his choices but he has brushed them off, still insisting his choices are perfect (according to the sales pitched offered by the sellers).
Not trying to be a wet blanket but be aware that many of these old timers and forummers are far more experienced and have tried many things in their day and definitely know what they are talking about and it would be worthwhile to take their opinions seriously.
Anyway, i wish you good luck and hope you can make your dreams come true. And anyway, as to building something that fulfils your needs, then I am pretty sure that what you intend to do here definitely far exceeds your needs easily, but is it necessary and at what cost? Power not used is basically power wasted. Just my two cents.
Sorry to come by so negatively, just did not want you to waste your time and money to discover that what you needed was just a simple 10W amp after all...
Don't get disgusted and quit when people are trying to help you.
Tone it down a little and start over. Maybe now is a good time to review your needs and goals with the gang.
It may help others understand where you are coming from and it may help you understand where you are going.
Like I said, everyone here wants to see you succeed. Win-win.
OK
First off I do not need this much power as I have said before!
I am doing this for the Wow factor, That is it, I have the drive and the $$ so now I need a good plan. I thought I was on the right track but I guess not,
Lets talk OPT
I have been told by others that these are very nice OPT and they are very capable of doing as I plan, Now the tubes may not be a good choice, So I am open to any and all suggestions on tubes, Also I need PT for this project. This same gent (Risson amps) said he has 2 PT made by Randell (anyone know this company) and were made for this setup. The paperwork above he said tells the specs of the PT
I cannot determine what the specs are.
First off I do not need this much power as I have said before!
I am doing this for the Wow factor, That is it, I have the drive and the $$ so now I need a good plan. I thought I was on the right track but I guess not,
Lets talk OPT
I have been told by others that these are very nice OPT and they are very capable of doing as I plan, Now the tubes may not be a good choice, So I am open to any and all suggestions on tubes, Also I need PT for this project. This same gent (Risson amps) said he has 2 PT made by Randell (anyone know this company) and were made for this setup. The paperwork above he said tells the specs of the PT
I cannot determine what the specs are.
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