I was actually thinking about just buying a pair and seeing if they sound good. The only test equipment I have are my ears. The local radio shack in my hometown actually spawned off of a small tv repair store. The guy who owns it I have become friends with and I know he has some equipment in back that he would show me how to use if I ever wanted. I figure it is a savings of a few dollars and it would be nice to try something other than Edcor with out having to break the bank.
Now as I peak into this box of tubes I just got I already spot a 6kd6 and a pair of 26LW6s. The best part of it all is when I left the guys house he said "Oh yeah I have one more shed to go through that is filled with Tvs from the 50s and there are a couple more boxes of tubes.
Now as I peak into this box of tubes I just got I already spot a 6kd6 and a pair of 26LW6s. The best part of it all is when I left the guys house he said "Oh yeah I have one more shed to go through that is filled with Tvs from the 50s and there are a couple more boxes of tubes.
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Well the 100 watt Antek has a published frequency response that is 2 db down at 20 KHz. That alone says "not great for HiFi" and may make some feedback systems unstable. I haven't heard of anyone using them. I have a set of absolutely huge 400 watt Plitrons and they are 2 db down at 60 KHz. A smaller toroid should be better. If I was going to purchase a set of P-P OPT's, my money would go to Edcor, but buying OPT's is not in the budget right now.
Well, we know that the 6KD6 will drop right into this board and make as much power as you want. I haven't tried the 'LW6's but I suspect that they will work. Some kind of socket adapter will be needed.
I have decided that if I build an amp with my board (it has to survive all of my experiments) I will use the 6HJ5's and one of two sets of OPT's that I have. One type of OPT is the "ugly" ones you guys have on your Simple P-P's. That is what I have been using for my testing and they sound good at up to 100WPC through my speakers.
TV's from the 50's were mostly black and white. The power transformers are suitable for reasonable sized stereo amps. The audio OPT is good for a couple of SE watts, and the vertical sweep OPT is good for maybe 5 SE watts. The vertical OPT's come in two types 3 wire (not too useful) and 4 wire (usually blue, red, black, and green). These make good SE OPT's. Color TV's have much bigger transformers. How do I know this? When I was young I used to build guitar amps out of old B&W TV's.
I'm probably in the same boat on both counts.
It doesn't seem like audio grade transformers are really their forte. It's almost like someone that works there builds tube amps as a hobby and they started winding a few OPTs on cores they already had. The HF response probably means it is wound like a power transformer. 🙂 Of course, so is this other transformer we have....
Anyway, Edcor has a plethora of primary impedances to pick from and so far I have no complaints about their quality. Also, from what I have read by the so-called experts here and elsewhere, E-I is that way to go for OPTs unless you really know what you are doing. Plitron is the Cadillac of OPTs.
Well it looks like I only got one 6kd6 in the box of tubes. So I am thinking I will base this around the 6HJ5s I have. I already have it laid out with the changes to the circuit so that seems the most affordable way to go. The 6kd6s are a bit spendy.
I thought about using those at least to test it out and make sure it is working correctly then perhaps decide on buying a pair of transformers dedicated for this amplifier and return those to the Simple PP.
Good to know, a friend and I built him a guitar amplifier a couple of weeks back. I know he wanted to build another one so perhaps something will come out of this pile that will fit the bill.
Very cool. My uncle claims to have a box of old tubes from his dad. I'm picturing a shoe box filled with old, worn TV tubes though. My father-in-law, on the other hand, has been cleaning his garage. I scored a non-working Heathkit IP-32 and a working Hammarlund HQ-140-X and a big box full of miscellaneous tube projects that way. He says he has a Harman Kardon amp in there that he knows has tubes in it. I can dream....
Indeed. My attempts to pry any other information about it have not been successful.
So Russ what are your thoughts on R21? I believe it is spec'd as a 5watt part but at the higher voltages you were seeing a dissipation of ~9 watts. I had found a 4.7k ohm 20 watt resistor in something I dissected.
On another note I got the power transformer ordered I just need to come up with a 100v CT transformer for the C-. I believe I read some where in this thread that you could also use just a 50volt supply and just use one of the rectifiers. I may be able to come up with a small 50volt transformer around the house if I look a bit through some of these boxes I got from this guy.
On another note I got the power transformer ordered I just need to come up with a 100v CT transformer for the C-. I believe I read some where in this thread that you could also use just a 50volt supply and just use one of the rectifiers. I may be able to come up with a small 50volt transformer around the house if I look a bit through some of these boxes I got from this guy.
That will work. I am using two 10k 7W resistors in parallel at the moment. The high dissipation only happened when the amp was at full output under test, presumably due to the screen currents of the tubes. At normal volume levels that isn't going to happen. That 20W resistor would be fine and I will probably use something similar that is aluminum housed so that it can be bolted to the chassis or a heatsink.
The bias supply puts out -60V, normally. I've setup C- with the bench supply to -70 and if I can safely use the 4TK400 then i will make use of the 70V taps and adjust R12 to give me the same -70V. If you use a 50V transformer, you'll need to use a bridge rectifier instead of the full-wave that is there now. It would probably be easier to locate the bridge outside of the PCB and just jumper the two diodes that are there.
The "stock" bias supply is technically 100VCT.
On the subject of the AN-4TK400...mine is labeled "AN-4TK400B". Although the wiring label isn't quite right, it actually has two 6.3V windings. One has a center tap. I measured them and that's indeed what they are. Perfect!
Jinxed myself. The HV secondaries are wired in parallel with each other, not mirrored. That means you can't tie them end-to-end and use a full wave rectifier on the 70V taps. Instead you end up with one 70V and one 330V tap. Grrr.
OK, I just couldn't wait. It worked like a charm. Had to start if off slowly because without load B+ was way too high for those 450V caps. However once biased and fully loaded, I was able to get the AN-4TK400B all the way up to line voltage. I do like how if the line voltage goes up, the bias voltage goes with it which biases the tubes colder. B+ settled in at 475V and C- was around -83V and clean (no noticeable increase in ripple running on the half-wave). It seemed to work out well, though the CCS's really need a heat sink at this point. Also the filter FETs were flaming hot after maybe 15 minutes of playing, even with a fan blowing on them. May need to tweak R21 a bit after all to take the strain off the screen regulator.
It was nice to see the amp off of life support, though, and running on its own. Sounded great still, of course.
It was nice to see the amp off of life support, though, and running on its own. Sounded great still, of course.
Ultralinear?
The iron for my DCPP is due from Edcor any day now (fingers crossed). In the meanwhile, I've been studying the schematic (like I understand even a fraction of Pete's design...not!) Anyway, the Edcor OPT's that Pete specs and the ones I'm getting, have screen taps. I'm assuming these are for UL operation. Now, Pete does not make any mention of UL in the construction notes, and I'm too much of a novice to know if UL works in this circuit or not.
Could one of you guys explain this to me?
The iron for my DCPP is due from Edcor any day now (fingers crossed). In the meanwhile, I've been studying the schematic (like I understand even a fraction of Pete's design...not!) Anyway, the Edcor OPT's that Pete specs and the ones I'm getting, have screen taps. I'm assuming these are for UL operation. Now, Pete does not make any mention of UL in the construction notes, and I'm too much of a novice to know if UL works in this circuit or not.
Could one of you guys explain this to me?
Not Ultralinear.
Pete designed this amp to use a regulated screen supply of +150V, not the voltage present from the UL taps. If you look at page one of the schem., you'll notice that there is a G2 (screen) +150V supply shown. This +150V also supplies the driver tube screens.
Jeff
Pete designed this amp to use a regulated screen supply of +150V, not the voltage present from the UL taps. If you look at page one of the schem., you'll notice that there is a G2 (screen) +150V supply shown. This +150V also supplies the driver tube screens.
Jeff
Yes, I get it. Thank you, Jeff!
So, would there be any advantage to a design that does use the UL taps?
(Pardon all the questions, but I'm still far short of having Morgan Jones committed to memory...😀 )
For a much better explanation than I can give:
An Ultra-Linear amplifier by David Hafler & Herbert I Keroes
Join the club.
Jeff
You can't hook the screens up to the UL taps because of the screen voltage limitation of most sweep tubes. These being something like 200V. The UL taps will have close to the plate voltage on them...slightly higher in fact. There is a trick you can do with zeners to get this to work, but there isn't much point.
Pete took some effort to get this design to work as designed and it works really well. UL is nothing more than a type of plate-to-screen feedback. Pete's board uses plate-to-grid feedback to accomplish the same thing...only better. I don't think you could take a sweep tube and get the same amount of linearity using UL than you can with plate-to-grid feedback. Sweep tubes were never intended for audio. Of course, I have no data to back my statement up...just my understanding of it.
Pete took some effort to get this design to work as designed and it works really well. UL is nothing more than a type of plate-to-screen feedback. Pete's board uses plate-to-grid feedback to accomplish the same thing...only better. I don't think you could take a sweep tube and get the same amount of linearity using UL than you can with plate-to-grid feedback. Sweep tubes were never intended for audio. Of course, I have no data to back my statement up...just my understanding of it.
Well I just received a bunch of 6HJ5s. Time to tear down the Simple PP and borrow the output transformers. I have been learning how to psudII a bit. Now just to put windows on my Macbook so I can use the software instead of having to go on my desktop. I received a box of transformers for free a little while ago so hopefully I can find something around 50volts for the bias otherwise I will see if antek has anything that will be suitable for that duty. I am still trying to envision a chassis for this amplifier. It is just so large of a board. Part of me wants to purchase one of those pre cut aluminum top plates you see on ebay but the other part of me has been searching for a dead vintage power supply to stuff this amp into.