Carl;
Interesting about the Rifa caps... Must investigate that.....
Well, guess there's nothing more to be said here.... Thanks to everyone! Espacially Mohan, Yves and Andrewbee. This is what this forum is all about!
I've updated the schematic on page 1 to reflect changes i've done / expereinced. (hit the 'refresh' button)
Stig Larsen of Norway!
Interesting about the Rifa caps... Must investigate that.....
Well, guess there's nothing more to be said here.... Thanks to everyone! Espacially Mohan, Yves and Andrewbee. This is what this forum is all about!
I've updated the schematic on page 1 to reflect changes i've done / expereinced. (hit the 'refresh' button)
Stig Larsen of Norway!
stigla said:Hello
I am wondering if anyone have buildt this amp:
http://www.meta-gizmo.com/Tri/interstage.html
I wonder if the rated 275V at the plates are correct. The amp states to give ~8W, and I think maybe the platevoltage should be 375V.
But then the 200uF PSU cap has a wrong Rating too..
The schematics give no currents, but I think it runs at 60mA per tube, thus giving a 60V bias through the 500R cathode resistor.
Anyone knows?
I really want to build this thingy, so I would appriciate some helpMaybe it gives 8W in class AB?
-Stig
Hello, Stigla:
Lundahl not recommend the LL1635 for SE to PP interestage xmer, instead use the LL1660 xmer.
Regards.
<b>Lundahl not recommend the LL1635 for SE to PP interestage xmer, instead use the LL1660 xmer.</b>
Yes, that's true. The LL1635 is for SE->SE or PP->PP only because it's winding pattern is not optimised for the SE->PP application.
There was a great section on www.diyparadiso.com about selection of the appropriate OP and IT transformaer from the Lundahl range. Their site is being reorganised so it was not available when I last checked tonight. Try again soon. Datasheets are available at www.lundahl.se
Yes, that's true. The LL1635 is for SE->SE or PP->PP only because it's winding pattern is not optimised for the SE->PP application.
There was a great section on www.diyparadiso.com about selection of the appropriate OP and IT transformaer from the Lundahl range. Their site is being reorganised so it was not available when I last checked tonight. Try again soon. Datasheets are available at www.lundahl.se
Hello!
Waking up an old tread here
Amps are running very good. I have dared to elevate the bias current of each tube to 60mA and around -47V gridbias. (two 750R's in parallell for the cathode resistor) and I really find this operating point more pleasing to my ears than the original.
I abandoned the Ultrapath at the input. Either the value I used was terrible wrong (22uF) or the particular ECC99's of mine was alergic to Ultrapath. Kind of removed details and softened the highs... so I sort of lost the interst in that and I did'nt really have any other values around to try out... Maybe I'll dig into it some other day.
Haven't got to try other caps for the PSU than the RIFA's either but I cant really recognise the things Carl Ekblom was talking about. But it is an interesting point and I will definitivley go into it some day. Maybe my ears are used to them 'couse I've got'em in my SS amp too!!
Had some problems with Arc-overs inside my 6D22S's on one channel. When I would fire up the amp, the Power tranny would "hum" for a sec or two, then a small "zzzzittt!" would appear inside one or both diodes, and then everything would work normal from there. (warmup time etc...) After some days this stopped happening, and I havent seen it since...
WEEEEEEELLLL anyway, enough "blah-blah". I have some really questions to ask you guys;
So. Take my schematic there, at the bottom of page 1. Would it be possible to throw in a couple of KT88, without any modifications besides a new Cathode resistor, heater arrangements and maybe some resistors from the plates to the screens?
What about running them in triode mode?
I'm just curious, if it's not TOO much work, I think it would have been fun to try out. Hopefully some more Output power, but thats not the main goal.
I've seen KT88 work with 5K loads in other amplifiers, and my OP-trannys can handle a good 50W, so the main limitation as I see it, would be the PSU. Too low voltage perhaps. Maybe I can gain som voltage by applying fixed bias through the IT sec. and connecting the cathodes to GND?
Of course, I want class A operation.
Stig
Waking up an old tread here
Amps are running very good. I have dared to elevate the bias current of each tube to 60mA and around -47V gridbias. (two 750R's in parallell for the cathode resistor) and I really find this operating point more pleasing to my ears than the original.
I abandoned the Ultrapath at the input. Either the value I used was terrible wrong (22uF) or the particular ECC99's of mine was alergic to Ultrapath. Kind of removed details and softened the highs... so I sort of lost the interst in that and I did'nt really have any other values around to try out... Maybe I'll dig into it some other day.
Haven't got to try other caps for the PSU than the RIFA's either but I cant really recognise the things Carl Ekblom was talking about. But it is an interesting point and I will definitivley go into it some day. Maybe my ears are used to them 'couse I've got'em in my SS amp too!!
Had some problems with Arc-overs inside my 6D22S's on one channel. When I would fire up the amp, the Power tranny would "hum" for a sec or two, then a small "zzzzittt!" would appear inside one or both diodes, and then everything would work normal from there. (warmup time etc...) After some days this stopped happening, and I havent seen it since...
WEEEEEEELLLL anyway, enough "blah-blah". I have some really questions to ask you guys;
So. Take my schematic there, at the bottom of page 1. Would it be possible to throw in a couple of KT88, without any modifications besides a new Cathode resistor, heater arrangements and maybe some resistors from the plates to the screens?
What about running them in triode mode?
I'm just curious, if it's not TOO much work, I think it would have been fun to try out. Hopefully some more Output power, but thats not the main goal.
I've seen KT88 work with 5K loads in other amplifiers, and my OP-trannys can handle a good 50W, so the main limitation as I see it, would be the PSU. Too low voltage perhaps. Maybe I can gain som voltage by applying fixed bias through the IT sec. and connecting the cathodes to GND?
Of course, I want class A operation.
Stig
Hi Stig,
Glad to hear you're enjoying the amps, and thanks for letting us know.
<b>So. Take my schematic there, at the bottom of page 1. Would it be possible to throw in a couple of KT88, without any modifications besides a new Cathode resistor, heater arrangements and maybe some resistors from the plates to the screens?</b>
Not really if you want significantly more power. For this tube I think you'd be needing 450Vp-k at 80-90 mA for class A and then you'd get about 16-20W output, about 5dBW more than you have now. The bias would be roughly the same, ~-45V, but the Rk's would need to be adjusted for the new Ik. Because a trioded KT88 isn't as linear as a 6B4G, you will also get 5-10x the distortion.
Running with the same B+ as you have now, I reckon maybe 10-12W, but I haven't run the curves, just glanced at them and guessed.
If your 6B4Gs are Sovteks, they have a high plate dissipation of 30W, not 15, and can take 450V on the plates. I'd change the PSU and run them a bit hotter if you really need the power, for say 10W. The difference betwen 6W and 10W is only 2.2dBW, hardly worth the effort.
Below are a set of KT88 triode curves for you to look at and try some loadlines on. An a full datasheet can be found at http://frank.nostalgiaair.org/sheets/084/k/KT88.pdf
Glad to hear you're enjoying the amps, and thanks for letting us know.
<b>So. Take my schematic there, at the bottom of page 1. Would it be possible to throw in a couple of KT88, without any modifications besides a new Cathode resistor, heater arrangements and maybe some resistors from the plates to the screens?</b>
Not really if you want significantly more power. For this tube I think you'd be needing 450Vp-k at 80-90 mA for class A and then you'd get about 16-20W output, about 5dBW more than you have now. The bias would be roughly the same, ~-45V, but the Rk's would need to be adjusted for the new Ik. Because a trioded KT88 isn't as linear as a 6B4G, you will also get 5-10x the distortion.
Running with the same B+ as you have now, I reckon maybe 10-12W, but I haven't run the curves, just glanced at them and guessed.
If your 6B4Gs are Sovteks, they have a high plate dissipation of 30W, not 15, and can take 450V on the plates. I'd change the PSU and run them a bit hotter if you really need the power, for say 10W. The difference betwen 6W and 10W is only 2.2dBW, hardly worth the effort.
Below are a set of KT88 triode curves for you to look at and try some loadlines on. An a full datasheet can be found at http://frank.nostalgiaair.org/sheets/084/k/KT88.pdf
Attachments
Re: KT88
I might just build some now as the small EL84PP amp I have will take them happily for about 3 X the power out. I have a whole lot of NOS VT100 JAN tubes from WW2, and a number of matched sets of later ones, maybe 50 in all. But I have no sockets or topcaps.
By the end of the week, my Allen Wright amps will be running, giving 12W. The transformers cleared Customs today. As part of this package are some custom power trans for a set of 813PP, trioded of course, which should give me 40W+ of thoriated tungsten DHT glory. I can't justify the power, but what the hell. The Fertin thread has me interested in trying some baffles, but even they only need a couple of watts.
Beautiful aren't they? Make 845's look like toys. More linear too.
(pic from Bas Hornemans site)
Cheers
Yes indeed I have. The STC datasheet from www.retrovox.com.au is excellent and has a full set of triode curves plus graphs showing the H2 and H3 as a function of input voltage fpr some op points. The curves look excellent, and I love the ST bottle and topcap, but they seem to be a particularly unloved tube. The DHTs, and the popular tets and pents are all you hear about.fdegrove said:
I might just build some now as the small EL84PP amp I have will take them happily for about 3 X the power out. I have a whole lot of NOS VT100 JAN tubes from WW2, and a number of matched sets of later ones, maybe 50 in all. But I have no sockets or topcaps.
I run horns (104+ dB/W), so power isn't an issue.If you need some more power than what a DHT Se amp has to offer I would most certainly consider using them.
By the end of the week, my Allen Wright amps will be running, giving 12W. The transformers cleared Customs today. As part of this package are some custom power trans for a set of 813PP, trioded of course, which should give me 40W+ of thoriated tungsten DHT glory. I can't justify the power, but what the hell. The Fertin thread has me interested in trying some baffles, but even they only need a couple of watts.
Beautiful aren't they? Make 845's look like toys. More linear too.
(pic from Bas Hornemans site)
Cheers
Attachments
813
People,
My guess is that as long as the real McCoy was around people did not want to complicate their life too much.
Keep on posting stuff like this though and you'll see what happens to the stock price.
Add to that the top cap and you start to see why some people are uncomfortable with this tube.
Rgds,
People,
My guess is that as long as the real McCoy was around people did not want to complicate their life too much.
Keep on posting stuff like this though and you'll see what happens to the stock price.
Add to that the top cap and you start to see why some people are uncomfortable with this tube.
Rgds,
807 and such
Fellows,
I have no idea in what way the presence of such a top cap might impede importation for safety regulation and so forth.
One thing I know is that it is a PITA and given any alternative inroads,any manufacturer will prefer the regular eq. to topcaps as such.
One designer who was bold enough to use the 807 was Mr.David Manley.
Importing them to Europe however often involved not so truthfull bills.
The point was however that many tubes are still around using such a top cap and can be had for a reasonable price,as a DIY audiophile you can often easily get by without adhering to strict laws at your own risk.
Caveat emptor.
Fellows,
I have no idea in what way the presence of such a top cap might impede importation for safety regulation and so forth.
One thing I know is that it is a PITA and given any alternative inroads,any manufacturer will prefer the regular eq. to topcaps as such.
One designer who was bold enough to use the 807 was Mr.David Manley.
Importing them to Europe however often involved not so truthfull bills.
The point was however that many tubes are still around using such a top cap and can be had for a reasonable price,as a DIY audiophile you can often easily get by without adhering to strict laws at your own risk.
Caveat emptor.
Hmmm, well.... it was just a thought. Guess Ill keep the 6B4G's, try to raise the current to, say, 75mA / tube at -45. This way I'll get the same OP power, but hopefully less distortion... Plate dissipation around 23W... (77%) of max.
This means ~0,195A from the PSU, and that should work fine.
I don't really need more power, as can practicly kill pepole with ~7W on my 98dB/W speakers (haven't tried it though)
The amps sound really really good. Cant describe how satisfied I am!
I resently discovered that RS-Components in UK sells ELNA Audio Grade ARD (Starget) caps. Guess Ill try some 100uF / 50Volters instead of the RIFA PEG124's I have now. Pretty cheap too!! (or maybe Panasonic's Superlow Impedance FA)
Any recomends conserning PSUcaps? In place of my current RIFA PEH200's? ELNA's normal Low imp series maybe? I have seen those caps in some comercial (SS) amps of high quality.
Interesting to read about the 807. I happen have 4 lighly used 1625's (RCABrownbase) laying around. Was thinking of making a guitar amp of them, but this little discussion down here gave me new thoughts. Though, I can't really see that they are very linear, especially in triode mode... (ain't this tube just a beefed up version of the 6L6?)
But the KT66 I have long wantet to use Saw that Sowter finaly have made a QuadII replacment OPT. If I ever get alot of cash, I will make a QuadII amp just for the fun of it. I like the looks!!
This means ~0,195A from the PSU, and that should work fine.
I don't really need more power, as can practicly kill pepole with ~7W on my 98dB/W speakers
(haven't tried it though) The amps sound really really good. Cant describe how satisfied I am!
I resently discovered that RS-Components in UK sells ELNA Audio Grade ARD (Starget) caps. Guess Ill try some 100uF / 50Volters instead of the RIFA PEG124's I have now. Pretty cheap too!! (or maybe Panasonic's Superlow Impedance FA)
Any recomends conserning PSUcaps? In place of my current RIFA PEH200's? ELNA's normal Low imp series maybe? I have seen those caps in some comercial (SS) amps of high quality.
Interesting to read about the 807. I happen have 4 lighly used 1625's (RCABrownbase) laying around. Was thinking of making a guitar amp of them, but this little discussion down here gave me new thoughts. Though, I can't really see that they are very linear, especially in triode mode... (ain't this tube just a beefed up version of the 6L6?)
But the KT66 I have long wantet to use
Saw that Sowter finaly have made a QuadII replacment OPT. If I ever get alot of cash, I will make a QuadII amp just for the fun of it. I like the looks!!
CAPS
Helllo Stigla,
Glad to see you're happy with the amps.
Regarding caps,and assuming you're talking about cathode decoupling:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=4621
Happy listening,
Helllo Stigla,
Glad to see you're happy with the amps.
Regarding caps,and assuming you're talking about cathode decoupling:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=4621
Happy listening,
Hello Stig
Good to hear that you like your amp. I nearly built one myself but finally ended up with a SE design. KT88 triode connected and 6C45 with LL1660 as interstage transformer and active regulated power supply for all tubes.
If this is to any help:
For powersupply caps I think that if you want a substantial improvement one way is to go for an all polypropylene powersupply. In scandinavia SCR/solen and MCap are available.
Regarding cathode decoupling caps I have found that Rubycon ZL (from farnell in UK) not are too bad. I use them today with a 10u SCR in parallel.
I have been using triode connected 6550/KT88 for several years now. I like them a lot. About the same power as 300B but easier to drive. I use them with 100-120mA through the tube and a fairly high impedance ratio, 9.6k:8 ohms for push pull. In the SE amplifier I use 3.3k:8 ohms.
Besides that I agree with you that the ECC99 really is a good sounding tube.
Regards
Carl
Good to hear that you like your amp. I nearly built one myself but finally ended up with a SE design. KT88 triode connected and 6C45 with LL1660 as interstage transformer and active regulated power supply for all tubes.
If this is to any help:
For powersupply caps I think that if you want a substantial improvement one way is to go for an all polypropylene powersupply. In scandinavia SCR/solen and MCap are available.
Regarding cathode decoupling caps I have found that Rubycon ZL (from farnell in UK) not are too bad. I use them today with a 10u SCR in parallel.
I have been using triode connected 6550/KT88 for several years now. I like them a lot. About the same power as 300B but easier to drive. I use them with 100-120mA through the tube and a fairly high impedance ratio, 9.6k:8 ohms for push pull. In the SE amplifier I use 3.3k:8 ohms.
Besides that I agree with you that the ECC99 really is a good sounding tube.
Regards
Carl
Hi 45,
That's Kurt Strain's PP45 amp there. All I know is it works, he liked it nearly as much as some of the all DHT SET parafeeds he used too, and better than his 845 PP. Lots of stuff 3 or 4 months back on the Asylum Tube DIY board.
The coupling caps into the primary of the IT are too small for fullfange, but he used it to drive the top half of his Oris horns (150Hz up). Later the driver was changed for the ECC99 with apparently good results.
You can easily modify it for 2A3's by changing the OPT to something with a Zp of about 5-6K, the 710R cathode bias the correct value for where you run the 2A3's, and maybe specify bigger heater windings on the power trans as the 2A3's draw more than 45's. Personally, I'd up the bias on the driver to about 20mA too. Both the ECC99 and 6H30 sound better there.
My hunch is it'll sound better than the Ralph Power design. Garry Dahl, who actually did the first version of that now uses a full PP setup (Olson Aurora's) with parafeed IT and CCS deiver loads. Keepind DC out of the trans could only work better IMO.
Do you have the schematic for his CCS, especially the last bootstrapped version? I lost mine in a HDD crash, and wanted to use them in something else.
Cheers
That's Kurt Strain's PP45 amp there. All I know is it works, he liked it nearly as much as some of the all DHT SET parafeeds he used too, and better than his 845 PP. Lots of stuff 3 or 4 months back on the Asylum Tube DIY board.
The coupling caps into the primary of the IT are too small for fullfange, but he used it to drive the top half of his Oris horns (150Hz up). Later the driver was changed for the ECC99 with apparently good results.
You can easily modify it for 2A3's by changing the OPT to something with a Zp of about 5-6K, the 710R cathode bias the correct value for where you run the 2A3's, and maybe specify bigger heater windings on the power trans as the 2A3's draw more than 45's. Personally, I'd up the bias on the driver to about 20mA too. Both the ECC99 and 6H30 sound better there.
My hunch is it'll sound better than the Ralph Power design. Garry Dahl, who actually did the first version of that now uses a full PP setup (Olson Aurora's) with parafeed IT and CCS deiver loads. Keepind DC out of the trans could only work better IMO.
Do you have the schematic for his CCS, especially the last bootstrapped version? I lost mine in a HDD crash, and wanted to use them in something else.
Cheers
<b>This is the one on my shortlist.
It's got this nice "look ma,no couplin'caps" feel to it.</b>
Frank,
Go 'whole hog' on it.
<b>Aurora Integrated</b>
<img src=http://www.aloha-audio.com/Amity-Integrated.gif>
And a pic to show how pretty it can be.
<img src=http://www.aloha-audio.com/aurora-garydahl.jpg>
Cheerio
It's got this nice "look ma,no couplin'caps" feel to it.</b>
Frank,
Go 'whole hog' on it.
<b>Aurora Integrated</b>
<img src=http://www.aloha-audio.com/Amity-Integrated.gif>
And a pic to show how pretty it can be.
<img src=http://www.aloha-audio.com/aurora-garydahl.jpg>
Cheerio
Sakuma-san
Frank,
Your pic didn't show up at first, before I made the last post, but I really like the design.
I'd really like to do a hybrid between Sakuma-sans 845 (there's another that's 845PP-IT-845PP) and Lynn's Aurora, losing the 6J5 and Sowter 9100.
This is how PP should be done. The IT's help with dynamic balance between the tubes, and the secondarys act as gridchokes, giving low DCR to ground for any grid current yet keeping a high Z.
I have all the iron.......
Cheers
Brett
Frank,
Your pic didn't show up at first, before I made the last post, but I really like the design.
I'd really like to do a hybrid between Sakuma-sans 845 (there's another that's 845PP-IT-845PP) and Lynn's Aurora, losing the 6J5 and Sowter 9100.
This is how PP should be done. The IT's help with dynamic balance between the tubes, and the secondarys act as gridchokes, giving low DCR to ground for any grid current yet keeping a high Z.
I have all the iron.......
Cheers
Brett
PP 845
Hey Brett,
I see we're both on the same channel again.
You're idea seems fine to me.
Lovely beasts!
What I don't quite get though is why he use uses such low plate voltage on the first stage.(see pic I posted)
Surely you can't reach full power that way.
Although in reality you'll probably not miss it.
What I love about these circuits is that you take one look and it all comes together.
"Elegance supreme".
Which proofs once more you really know an incredible lot about tubes.
See you.
Hey Brett,
I see we're both on the same channel again.
You're idea seems fine to me.
Lovely beasts!
What I don't quite get though is why he use uses such low plate voltage on the first stage.(see pic I posted)
Surely you can't reach full power that way.
Although in reality you'll probably not miss it.
What I love about these circuits is that you take one look and it all comes together.
"Elegance supreme".
Which proofs once more you really know an incredible lot about tubes.
See you.
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