807 vs. 1624 tetrode ?

[coresta]

Rcavictim, do you think UL to be a real improvment ? On curves maybe, on sound , i don't believe it anymore . I tested EL84, EL34, 6L6 . I now prefer gasVR toobz in screens , even "less undistorded power" . cheers

[Giaime]

Do you really???

I've got to try, I could use cheap toroidals for the OTs in my EL84PP which don't have UL taps

[rcavictim]

Originally posted by coresta
Rcavictim, do you think UL to be a real improvment ? On curves maybe, on sound , i don't believe it anymore . I tested EL84, EL34, 6L6 . I now prefer gasVR toobz in screens , even "less undistorded power" . cheers

I don't have much experience with straight P-P pentode sound so I'm not a good authority to ask if UL is better. I do know that UL makes for an easier to build amp because it eliminates the need for regulated screen supplies. I also know that with fixed screen supply you can get more output power from any given pair of output bottles than in UL. It is also easier to drive straight P-P without the NFB created by the UL tap as less grid swing is needed.

I've been exploring SET mode in recent years although I keep calibrated by listening to a MC34B MingDa P-P UL amp which has really fine sound with old Mullard 6CA7's inatalled.

[rcavictim]

Originally posted by Giaime
Do you really???

I've got to try, I could use cheap toroidals for the OTs in my EL84PP which don't have UL taps

Pentodes and tetrodes require a much higher plate Z load than triodes typically do. Even with triodes it is almost impossible to find torroidal power xfmers with enough L to load properly in a plate circuit. Spme low plate resistance triodes like 6080 are the exception. Cathode loading of the output stage is a possibility with re-purposed toroids, but that is a mode that requires big driver voltage swing and associated design/implementation headaches.

[Shoog]

May I point you to the following article by Steve Bench, which proves that toroidals can be used for both input and output duties. I have done a little test with a 110:24V trans and got good response down to 20hz

ttp://members.aol.com/sbench/50c5.html


Shoog

[rcavictim]

Originally posted by Shoog
May I point you to the following article by Steve Bench, which proves that toroidals can be used for both input and output duties. I have done a little test with a 110:24V trans and got good response down to 20hz

ttp://members.aol.com/sbench/50c5.html


Shoog

Well actually, it's not polite to point.

Seriously though, Steve B. only asked 1:1 duty for his toroid turned input xfmer, and that buys a lot of performance. .Stepdown even more-so. You want to step UP. He didn't mention what he used to drive the input xfmer either

On the output transformer he specifically mentions that the toroid was unable to give a high enough load Z to the output tube plates and output power was lost as a result.

At this stage I think you are ready to start breadboarding an actual circuit and start measuring actual performance with the tubes and toroids you wish to use. Further discussion would likely please acamedics, who at the end of the day don't need a connection with reality, but you appear to be after an actual working hardware amplifier.

[Shoog]

Certainly our discussion has been very educational and informative. You might notice that after digesting your advise I myself am now proposing a 1:1+1 or 1:2+2. I have also taken on board the fact that as outputs they are the weak link and will need to be replaced at some point. Still they will perform well down to 50hz at least, which is quite adequate for a lot of applications and as an experimental test bed, which is what mine will be.
I will report back when I have some useful data.

Shoog

[rcavictim]

Well I don't mind helping a fellow DIY'er understand stuff if I can. It has helped me a bit by making me think about stuff that I usually don't give much thought. I have to give my hands most of the credit. My hands are pretty good at building things and I just exist to get them to the workshop on time when they itch with inspiration. I'm not very good at taking notes of what they are doing, so some of the fancy technical challenges they have overcome are not as well understood by me to put into words as they might be. Now, I'd be really lost if my hands weren't here typing my responses for me.

Go breathe some solder flux fumes and let us know how you make out.

[Miles Prower]

Originally posted by coresta
Rcavictim, do you think UL to be a real improvment ? On curves maybe, on sound , i don't believe it anymore . I tested EL84, EL34, 6L6 . I now prefer gasVR toobz in screens , even "less undistorded power" . cheers

UL was a clever scheme, however, I believe its benefits to be over rated. Better to use regulate the screen voltage on your pentode finals, and add parallel feedback from the plates to drivers. That way, you get the benefits of Zo reduction, and tweaking it for the best sound is only a matter of replacing a resistor. With UL, once the xfmr is wound, the die is cast, and there's no going back without either replacing the entire xfmr, or rewinding the whole primary.

[coresta]

Yes, just add some OA2 or OB2 in screen, these are more sexy than zeners and look at AudioResarch or ... Western Electric schematics Happy listening