Heya Jeff,
Ooooookay, one of them things... 7591... yeah, 6K6 OPT.
Thanks for the info
Cheers!
Ooooookay, one of them things... 7591... yeah, 6K6 OPT.
Thanks for the info
Cheers!
I have a fully restored Eico ST-70 with some recommended enhancements from David Gillespie. I can say the irons are indeed quite decent. These 2 are from another ST-70 that I picked up from a garage sale.
Since these OPT don't have UL tap, this amp from Pete and Miles 6BQ6GTB/807 pentode are my final choices. Pete's PCB makes the build a lot easier, but the 6BQ6GTB and the 807 tube are close to the 7591 which are the OPT was designed for. Tough choice.
Since these OPT don't have UL tap, this amp from Pete and Miles 6BQ6GTB/807 pentode are my final choices. Pete's PCB makes the build a lot easier, but the 6BQ6GTB and the 807 tube are close to the 7591 which are the OPT was designed for. Tough choice.
Last edited:
Hi Fred,
I know the 806 likes much as the 6L6 family does, but I thought Miles was using 4400 ohms A-A for his 6BQ6 beauty?
Cheers!
I know the 806 likes much as the 6L6 family does, but I thought Miles was using 4400 ohms A-A for his 6BQ6 beauty?
Cheers!
Huh? I guess you must have meant 807 there. The 806 is something much different.
I thought Miles was using 4400 ohms A-A for his 6BQ6 beauty?
That's what it does use: 4K4 (P-2-P). Given the plate characteristics, a 6K6 (P-2-P) would put you way down on the characteristic, and away from the most linear part. 6K6 would probably be more apropos to much higher voltages and Class B or Class C for an RF amp.
There was one Portugese (Brazilian?) deisgn for an AM plate modulator that got 70W of audio from a PP pair of 6BQ6GTBs, but it was deep into Class AB, and definitely not designed with sonic excellence in mind (which is not legal on the ham bands anyway).
Last edited:
My bad... my brain was two tabs over from when I posted
Now I have some 4.3K-ish Dynaco iron here, I can play with your design some
Cheers!
Last edited:
I would expect the ceramic would do fine. I put the caps there because there was some tendency to oscillate if the OPT leads were very long - not sure exactly what the FB path was. Also tended to optimize the square wave response and damp any ringing. You may not even need them...
Pete
I got these today, they are tall and skinny, and they fit the board just fine. Unfortunately, now they are all sold out!
I got some of these too, but they are short and fat and cover up some surrounding components. They will work in a low profile version of the Simple P-P which is why I got them. I didn't order any other caps this time.
Attachments
Thanks for the parts tips. The customer support at Allied is excellent. I got a bunch of 470uF 450v's for a bargain a while back.
I notice that 862-6212 is a likely skinnier 82uF.
I also figure 507-0802 is a compromise to the mica equivalent, but is significantly less expensive.
I figure I can kludge in 586-0378 in positions C22 and C30. Won't be pretty at all.
For the top caps, I got a choice of some hefty coax where the center is Teflon insulated (don't know voltage rating) or 22awg 600v wire. I figure for extra safety on the latter I could fish it through some insulating tubing.
I notice that 862-6212 is a likely skinnier 82uF.
I also figure 507-0802 is a compromise to the mica equivalent, but is significantly less expensive.
I figure I can kludge in 586-0378 in positions C22 and C30. Won't be pretty at all.
For the top caps, I got a choice of some hefty coax where the center is Teflon insulated (don't know voltage rating) or 22awg 600v wire. I figure for extra safety on the latter I could fish it through some insulating tubing.
Last edited:
but will my snivets show?
http://www.diyaudio.com/forums/showthread.php?p=229627&highlight=snivet#post229627
http://www.diyaudio.com/forums/showthread.php?p=229627&highlight=snivet#post229627
That depends.
No surprise that these TV veterans mention the 6BG6GT specifically. This type is an 807 with an octal base. The 807 is notorious for producing these things, and I had that exact problem when using 807s as Class AB1, PP finals. They showed up while o'scoping as a damped oscillation of about 60KHz at plate cutoff.
Adding 1K5 screen stoppers fixed that little problem. With 6BQ6GTBs, these did not appear, but I added 680R screen stoppers just in case.
Our local Wal Mart {evil} has a really nice heavy aluminium cake pan for $14us.
If you arent' concerned about asthetics they look really fine. I plan on using it for the chassis of my tube parametric test set.
Scratch the cake pan -- I have a chassis for an HP5328 Frequency Counter which was adapted by an oil-service company -- and they managed to fry it -- it can be shortened up by trimming the rails -- nice and sturdy -- will fit the transformers and PCB quite easily:
An externally hosted image should be here but it was not working when we last tested it.
Hello, I have several Novice questions?
How will this amp behave with 6 Ohm speakers.
I am confused since edcor page says that the CXPP25-MS-8K transformers are designed for 4, 8, 16 ohms.
I will be powering the amp from 220VAC, wouldn't I need to change the IEC inlet fuse value, to 1A, instead of the 2A specified on the BOM?
Thanks in advance.
How will this amp behave with 6 Ohm speakers.
I am confused since edcor page says that the CXPP25-MS-8K transformers are designed for 4, 8, 16 ohms.
I will be powering the amp from 220VAC, wouldn't I need to change the IEC inlet fuse value, to 1A, instead of the 2A specified on the BOM?
Thanks in advance.
If you connect 6 ohm speakers to the 8 ohm tap then the output tubes will see a 6k primary, if you connect them to the 4 ohm tap they will see a 10k primary. But from what I have learned, if these are commercial speakers rated as 6 ohm, they are probably closer to 4 ohm anyway.
Since 8k is still a pretty high load impedance for the output tubes, I suspect the 8 ohm taps would be fine with your 6 ohm speakers. But you can try both, or even connect both to binding posts so you can easily change between them. That is an advantage of the "multi-secondary" output transformer.
You might want to change the fuse to 1A for 240V operation. The only possible issue is that even though the average current goes down, the inrush (when you first turn on the amp) might go up (on 240V vs. 120V). You definitely need a slow-blow (time delay) fuse.
Pete