“Couldn't it be - at least from Alexander Dumble's perspective - that in a guitar amplifier with - as it says here in the opening post - an "output power rated @ 137 watts" - a different wiring of the output transformer may make sense than with a bass amplifier rated @ 220 watts?”
But unfortunately (from my perspective) I have not yet received an answer to this question (or perhaps no answer that did understand?). Therefore, your assumption "Now you know" unfortunately does not yet apply.
But please don't misunderstand me now: Of course, nobody here should feel obliged to answer my questions. But of course it would be nice (from my perspective).
Max, afaik you cant get 220w out of 4x or 6X 6550 tubes. It's how the voltage is divided over the plate and screen grid what Tony is talking about with the UL taps on the OT. This can be done with 2x 6550 and also with 4x6550 and with 6x6550.
Its ultimate guessing what is used, if nobody confirms.
So what do you think how this could be wired, preferable with a schematic? No links; just what you think.
First of all thanks for trying to explain this to me in a way I may understand. In the first small step I would like to find out now if I correctly understand what you have written:
Do I understand you correctly that from an electrical engineering point of view it is only possible to achieve the output power of 220W reported by Michael Husser with the 4 x KT88 tubes of the Winterland #003 when using the UL-taps of the A451?
Or did you mean that even when using the UL taps of the A451 it is completely impossible to achieve an output power of 220W with the 4 KT88 of the Winterland #003 and that the information provided by Michael Husser in this regard is therefore possibly a bit exaggerated?
Max wrote: ↑Wed Apr 21, 2021 1:48 pm
First of all thanks for trying to explain this to me in a way I may understand. In the first small step I would like to find out now if I correctly understand what you have written:
Do I understand you correctly that from an electrical engineering point of view it is only possible to achieve the output power of 220W reported by Michael Husser with the 4 x KT88 tubes of the Winterland #003 when using the UL-taps of the A451?
Or did you mean that even when using the UL taps of the A451 it is completely impossible to achieve an output power of 220W with the 4 KT88 of the Winterland #003 and that the information provided by Michael Husser in this regard is therefore possibly a bit exaggerated?
Thanks again and best regards,
Max
we're not talking about KT88, were talking about the 6550 tubes and the UL taps of the OT schematic. How would you wire the 6550 tubes without the UL taps, as you add a possibility the UL taps arent used, despite the high voltage. Preferably in a schematic?
erwin_ve wrote: ↑Wed Apr 21, 2021 12:28 pm
Max, afaik you cant get 220w out of 4x or 6X 6550 tubes. It's how the voltage is divided over the plate and screen grid what Tony is talking about with the UL taps on the OT. This can be done with 2x 6550 and also with 4x6550 and with 6x6550.
Its ultimate guessing what is used, if nobody confirms.
So what do you think how this could be wired, preferable with a schematic? No links; just what you think.
Max wrote: ↑Wed Apr 21, 2021 1:48 pm
First of all thanks for trying to explain this to me in a way I may understand. In the first small step I would like to find out now if I correctly understand what you have written:
Do I understand you correctly that from an electrical engineering point of view it is only possible to achieve the output power of 220W reported by Michael Husser with the 4 x KT88 tubes of the Winterland #003 when using the UL-taps of the A451?
Or did you mean that even when using the UL taps of the A451 it is completely impossible to achieve an output power of 220W with the 4 KT88 of the Winterland #003 and that the information provided by Michael Husser in this regard is therefore possibly a bit exaggerated?
Thanks again and best regards,
Max
Quite certain one can achieve 220W with bandwidth narrowed to 30Hz-15kHz frequency. With 800VAC into silicon rectification plus quad of KT88 the engineering maths tally. The engineering marketing from David Hafler puts the design at 240W operating point. This all works whether UL or otherwise. There will be differences in distortion and more. Personally interested in following the UL model.
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UL or not really doesn't matter. Plate voltage and load impedance are the main factors determining output power. Screen voltage has to be brought down, either using a distributed load (UL) or a separate screen supply. With 550V on the plates and 2k ohm primary impedance, 4x 6550 or KT88 will produce (on paper) nearly 250W.
You can of course be more conservative: 6550 data sheet (GE) shows 70W for a pair at 450V in UL 4k Zpri, 77W for fixed bias and 3500 Zpri.
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For anyone with the interest and a copy of Kevin O'Connor's TUT Vol. 6 on the shelf suggest studied reading of chapter five. The subject is engineering detail underpinning his design of a 400W amp around 6xKT88. It does require correctly spec'ed power & output transformers, and does achieve > 120W per KT88 pair. The question of why is left unanswered of course.
Do I understand your explanations correctly to the effect that, with regard to the circuit of the Dumbleland Special 150W #009, both variants would be conceivable in principle, namely a distributed load (UL) or a separate screen supply, but that Aaron and talbany (and perhaps others too) think it is much more likely that Alexander Dumble decided against a separate screen supply and for a distributed load (UL)? Or have I misunderstood that?
Max wrote: ↑Wed Apr 21, 2021 6:56 pm
Thank you for your explanations.
Do I understand your explanations correctly to the effect that, with regard to the circuit of the Dumbleland Special 150W #009, both variants would be conceivable in principle, namely a distributed load (UL) or a separate screen supply, but that Aaron and talbany (and perhaps others too) think it is much more likely that Alexander Dumble decided against a separate screen supply and for a distributed load (UL)? Or have I misunderstood that?
Thanks again and best regards,
Max
That's what it sounded like to me yes. It makes sense that if you have a transformer that already has UL taps to use them instead of need to add significant other components to drop the voltage significantly enough to be in the range to not cook the screens of the 6550. As I recall you need to be like 300VDC or lower for non ultra linear operation and in UL you get a bit more room like 400VDC, but you also get more output and cleaner headroom with the UL operation.
I.e. it's a win, win, win.
Lower screen voltage, better linearity, and better output power. This is why it's so favorable for HiFi, but not often used in guitar amps because the even order harmonics cause the amp to operate much more 'sing song' like with feedback you want in a guitar amp... But these amps do seem to be more focused on the HiFi and cleaner tones on purpose. Unlike the ODS types. BUT I have way less experience here, and I might be completely up in the night
Max wrote: ↑Wed Apr 21, 2021 6:56 pm
Thank you for your explanations.
Do I understand your explanations correctly to the effect that, with regard to the circuit of the Dumbleland Special 150W #009, both variants would be conceivable in principle, namely a distributed load (UL) or a separate screen supply, but that Aaron and talbany (and perhaps others too) think it is much more likely that Alexander Dumble decided against a separate screen supply and for a distributed load (UL)? Or have I misunderstood that?
That's what it sounded like to me yes. It makes sense that if you have a transformer that already has UL taps to use them instead of need to add significant other components to drop the voltage significantly enough to be in the range to not cook the screens of the 6550. As I recall you need to be like 300VDC or lower for non ultra linear operation and in UL you get a bit more room like 400VDC, but you also get more output and cleaner headroom with the UL operation.
I.e. it's a win, win, win.
Lower screen voltage, better linearity, and better output power. This is why it's so favorable for HiFi, but not often used in guitar amps because the even order harmonics cause the amp to operate much more 'sing song' like with feedback you want in a guitar amp... But these amps do seem to be more focused on the HiFi and cleaner tones on purpose. Unlike the ODS types. BUT I have way less experience here, and I might be completely up in the night
Happily being quoted with modestly qualified yes. The UL model is certainly simpler, as you'd sketched Phil. And arguably a somewhat more stable, both moment to moment when working and over shelf life of the amp. My take on the base Dumble formula is clear high headroom power. With the ODS a controlled preamp "gain" distortion colours the formula.
So I guess in my head my ods clean channels I've built are very guitar 'clean' but still have some of that 'grit' to them, but I do fully agree the majority of the tone in an ODS comes in the preamp. That being said, I've never felt the ODS power section is super different from most other fender designs, but I'm probably mistaken
Here you go Max
P.T off the Winterland
Find a Dynaco Catalog look up the spec's then get out your tube data sheets on the 6550 and do a little engineering.
I would be interested to know what plate voltages that bad boy is running and what kind of power it' capable of generating (compare it to #009) and confirm why he went with the taps..Maybe we can learn something along the way
Winterland.jpeg
Tony
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Last edited by talbany on Wed Apr 21, 2021 10:47 pm, edited 3 times in total.
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Wed Apr 21, 2021 10:14 pm
Here you go Max
P.T off the Winterland
Find a Dynaco Catalog look up the spec's then get out your tube data sheets on the 6550 and do a little engineering.
I would be interested to know what plate voltages that bad boy is running and what kind of power it generates and why he went with the taps..Maybe we can learn something along the way
pompeiisneaks wrote: ↑Wed Apr 21, 2021 7:11 pmThat's what it sounded like to me yes. It makes sense that if you have a transformer that already has UL taps to use them instead of need to add significant other components to drop the voltage significantly enough to be in the range to not cook the screens of the 6550.
Thank you for confirming that I have correctly understood your explanations as to why the UL version was included in the "Dumbleland Special 150W Schematic" proposed by Aaron and talbany. And of course it makes sense to start with the initial hypothesis that you think is the most likely.
So once again, thanks to you all for your explanations and best regards,
I am not going off on a big tirade about U.L here but a few things i'll address concerning the "Accent" switch and those thinking of using Fender U.L style transformers people might want to think about if they are considering using their transformers.
"Ultralinear" operation uses local negative feedback to the screen grids of the output stage by means of a tapped output transformer primary. This increases the damping factor and makes the amp tighter without the use of a global negative feedback loop.That being said, UL gets a bad rep in guitar amps because of the tragedies that were 1970s amp design. Namely, Fender botched by running (pseudo) UL and throwing in large amounts of global nfb ("presence")on top of U.L operation. you can use global negative feedback with ultra linear output stages, but you might not like the tone (Sterile).The accent switch enables you to completely remove the GNFB if you wish and I also recommend you experiment around with the GNFB resistor to adjust the right amount of NFB with it engaged and remember a little goes a long way in U.L Another alternative would be to axe the GNFB and add a cut control ala Vox.
Also something I recently read about Fenders U.L O.P.T..I cannot vouch for this?, however does make sense with respect to his quote (specifically) on output power??
Fender amplifiers employing a tapped screen output transformer are just that -- a tapped screen output transformer design that provides nothing like Ultra-Linear operation for the tubes. The proof is in the power output Fender achieved with their tapped screen grid operation. True Ultra-Linear operation with 6L6 tubes is specifically designated by its inventors to operate with the screen taps placed at 43% of the primary winding -- where the low order distortion and low output impedance of triode operation is still largely maintained, while a significant portion of the power output obtainable with pentode operation is still maintained as well. With the screen grids operating at that tapping point however, the most power that can possibly be squeezed out of a pair of 6L6 family tubes is 40 watts -- and they are fully squeezed to get that. Much more typical is about 30 watts or so -- yet Fender reliably got 70 watts with their tapped screen operation. That's because the tubes are NOT running in UL mode, but are operating with the screens powered from primary winding taps placed at (only) about 12.5% of the winding -- enough to eliminate the need for a filter choke in those models and prevent the screen grids from being over dissipated, yet not tapped so high as to be a detriment to power output.
