I was going to add but forgot to say that a tech friend of mine remined me that this type of PSU, where a low impedance regulated PSU designed to deliver current is stood on top of a high voltage PSU that is quiet but has no current delivery requirements is basically the same as old tellys and presumable scopes and anything else that uses a CRT. It does seems what goes around comes around. Or there's not much new is this game.
cheers,
-- Andrew
RIAA 1k5 LCR
#17
OK overheating solid state parts are not good, so I ordered just about the biggest heatsinks that Rapid had, tv40. I fitted them just a few days ago and have been away.
In spare moment, now were back, and when the kids were otherwise occupied. I managed to get 225v steady through a 5k load, so 45mA, for about 5 minutes and I could still touch the MJE350 heatsink. I can feel some heat above the PCBs, but nothing unexpected, this is more promising.
Onwards, slowly......onwards...
In the same order I got one of their double bobbin 0v-9v/0v-9v TXs, I reckon the Hammond ones are better made, but this was cheap enough. No instructions, however! And the data sheet on the site has little in the way of instructions. Now, I'm pretty certain that for center tapped usage I still short the middle two pins on the secondaries that are marked 9v (top of one bobbin) and 0v (bottom of the other), respectively, to ground . And then take power from the bottom of the lower bobbing and the top of the upper bobbin. Does that make sense? I do like to be certain of these things.
cheers,
-- Andrew
cheers,
-- Andrew
In spare moment, now were back, and when the kids were otherwise occupied. I managed to get 225v steady through a 5k load, so 45mA, for about 5 minutes and I could still touch the MJE350 heatsink. I can feel some heat above the PCBs, but nothing unexpected, this is more promising.
Onwards, slowly......onwards...
In the same order I got one of their double bobbin 0v-9v/0v-9v TXs, I reckon the Hammond ones are better made, but this was cheap enough. No instructions, however! And the data sheet on the site has little in the way of instructions. Now, I'm pretty certain that for center tapped usage I still short the middle two pins on the secondaries that are marked 9v (top of one bobbin) and 0v (bottom of the other), respectively, to ground . And then take power from the bottom of the lower bobbing and the top of the upper bobbin. Does that make sense? I do like to be certain of these things.
cheers,
-- Andrew
cheers,
-- Andrew
-
simon
- Thermionic Monk Status
- Posts: 5643
- Joined: Thu May 24, 2007 11:22 am
- Location: People's Republic of South Yorkshire
#18
Hi Andrew,
I also have a pair of the 0-9V TXs
. I'll be honest, I was in a rush to complete my order before Rapid's recent deadline and didn't look too closely.
This is probably going to be a rather silly question but by making a centre tap are you aiming for a 18V supply? Or have I got the wrong end of the stick?
Simon.
I also have a pair of the 0-9V TXs
. I'll be honest, I was in a rush to complete my order before Rapid's recent deadline and didn't look too closely.This is probably going to be a rather silly question but by making a centre tap are you aiming for a 18V supply? Or have I got the wrong end of the stick?
Simon.
#19
Hi Simon,
Yes, sounds like the same TX, mine was labelled 0v-9v and 0v-9v, on separate windings, that was what attracted me, my plan was, by joining the lower 9v with the upper 0v I was going to make a 9v-0v-9v or put it another way a 9v center tap. That does give 18volts but the two windings are in antiphase, well that's the plan, so configured for full wave rectification, of you see what I mean.
cheers,
-- Andrew
Yes, sounds like the same TX, mine was labelled 0v-9v and 0v-9v, on separate windings, that was what attracted me, my plan was, by joining the lower 9v with the upper 0v I was going to make a 9v-0v-9v or put it another way a 9v center tap. That does give 18volts but the two windings are in antiphase, well that's the plan, so configured for full wave rectification, of you see what I mean.
cheers,
-- Andrew
#21
OK, next step accomplished, new 9v tx from Rapid powers the two regulated DC supplies fine, one for the Aikido and the other for the input pentodes.
The Aikido needed one of those tv40 heatsinks before I was completely happy, with a 12v supply there was too much work for the regulator but the Aikido is doing roughly 2.4 Amps all on its lonesome 2x either 6N30 or 6N6P and 2 x either ECC83 or 5751 or 6072A etc so quite a lot of power being dissapated even at 9v and with some RC smoothing before the reg.
The RIAA modules are still not tested but I'm developing some VB scripts using Excel to drive some test gear at work. Having done one module manually made me realize some automation was in order. The scripts also follow Nick's suggestion of testing not only freq resp against ideal but also at varying amplitudes, which is the hard bit to get right for the chokes.
Can I resist not hooking it up this weekend and seeing what happens? Well I'm still a bit uncomfortable with the solid state supplies, I need some bigger wattage resistors on the HT protection circuit. I'll see what time I get spare from DIY duty on the bathroom and time with the kids etc.
Onwards...slowly onwards...
-- Andrew
The Aikido needed one of those tv40 heatsinks before I was completely happy, with a 12v supply there was too much work for the regulator but the Aikido is doing roughly 2.4 Amps all on its lonesome 2x either 6N30 or 6N6P and 2 x either ECC83 or 5751 or 6072A etc so quite a lot of power being dissapated even at 9v and with some RC smoothing before the reg.
The RIAA modules are still not tested but I'm developing some VB scripts using Excel to drive some test gear at work. Having done one module manually made me realize some automation was in order. The scripts also follow Nick's suggestion of testing not only freq resp against ideal but also at varying amplitudes, which is the hard bit to get right for the chokes.
Can I resist not hooking it up this weekend and seeing what happens? Well I'm still a bit uncomfortable with the solid state supplies, I need some bigger wattage resistors on the HT protection circuit. I'll see what time I get spare from DIY duty on the bathroom and time with the kids etc.
Onwards...slowly onwards...
-- Andrew
#22
Ok, it works......but bad news and good news.....
The bad news is it hums like a good 'un well much much more than my other phono(s)......the good news is that it seems to be confined to one channel only, and when I pull the phono plug on that channel out just a bit (signal connected but not ground) the hum is much reduced.
So, to me that implies that (assuming I'm right)...
...the design is not at fault (it could still sound crap) but the implementation is and I have ground loop on the bad channel.
Time to bring on the scope....
-- Andrew
The bad news is it hums like a good 'un well much much more than my other phono(s)......the good news is that it seems to be confined to one channel only, and when I pull the phono plug on that channel out just a bit (signal connected but not ground) the hum is much reduced.
So, to me that implies that (assuming I'm right)...
...the design is not at fault (it could still sound crap) but the implementation is and I have ground loop on the bad channel.
Time to bring on the scope....
-- Andrew
#23
So I went back and looked at both of T's LCRs and now the reason for the slight unorthodox biasing arrangements on the input pentodes on both versions becomes clear. Sometimes you have to build it to understand it. 
-- Andrew
-- Andrew
#24
Yep, I went through the same process with that part of the circuit. I also had to build it, and get it working with my stepup TX's to understand it.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#25
Well, it makes sound, but I wouldn't call it working.
I didn't copy T's circuit, because I didn't undestand it, I just used a normal pentode arrangement, after all, thought I, my load is 2.5 times higher, so I thought I could get away with it. Perhaps I should have, copied his design...but there you go, live and learn.
Seems he was trying to avoid both degenerative feedback and maximize gain from the pentode. In the mk2 he didn't even bother with a cathode resistor, he seems to think the grid current wouldn't be a problem.
I have a couple of LEDs ready to go in on the D3a's when I finish my DIY jobs. I'm sticking with orthodox, but modern, even if I do now understand why he did what he did; still there's plenty of time for tweaking....so I may try his arrangement, there's really very little HT on that pentode in the mk2, about 70v.
cheers,
-- Andrew
I didn't copy T's circuit, because I didn't undestand it, I just used a normal pentode arrangement, after all, thought I, my load is 2.5 times higher, so I thought I could get away with it. Perhaps I should have, copied his design...but there you go, live and learn.
Seems he was trying to avoid both degenerative feedback and maximize gain from the pentode. In the mk2 he didn't even bother with a cathode resistor, he seems to think the grid current wouldn't be a problem.
I have a couple of LEDs ready to go in on the D3a's when I finish my DIY jobs. I'm sticking with orthodox, but modern, even if I do now understand why he did what he did; still there's plenty of time for tweaking....so I may try his arrangement, there's really very little HT on that pentode in the mk2, about 70v.
cheers,
-- Andrew
Last edited by Andrew on Sun Aug 12, 2007 2:41 pm, edited 1 time in total.
#26
But as long as the grid is negativly biased, there won't be any grid current worth worrying about. The potential div that supplies the grid should apply -ve voltage to the secondary of the TX, so there is no current.Seems he was trying to avoid both degenerative feedback and maximize gain from the pentode. In the mk2 he didn't even bother with a cathode resistor, he seems to think the grid current wouldn't be a problem.
(unless I am thinking about a different circuit)
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#28
Ok, so I was thinking about a different circuit .
It worries me the grid bias in the first stage. I remember helping someone with a phonoII that for some reason was breaking cartridges. It turned uut there was a half a volt or so on the output of one chan from a gasey ecc83, that was enough to knacker the high output moving coil that was used.
.It worries me the grid bias in the first stage. I remember helping someone with a phonoII that for some reason was breaking cartridges. It turned uut there was a half a volt or so on the output of one chan from a gasey ecc83, that was enough to knacker the high output moving coil that was used.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#29
Well me too, that's why I wanted to take a more orthodox approach. In fact, someone questioned T about this on the thread where he detailed the mk2 and in the end all agreed it was probably OK if you used a step up TX that can isolate - not everyone wants or has one of those.
The bit I had missed was that T had avoided the degenerative feedback by not having a cathode R at all, but to me that just moves the problem, that's just my opinion, of course.
cheers,
-- Andrew
The bit I had missed was that T had avoided the degenerative feedback by not having a cathode R at all, but to me that just moves the problem, that's just my opinion, of course.
cheers,
-- Andrew
#30
Bad day or rather two or three bad days.
The old scope I use has given up the ghost, I just as I was getting somewhere 100Meg time base delay dual channel irreplaceable.
And during my initial experiments a couple of weeks ago I must have taken out either the voltage reference for voltage buffer op amp or the op amp itself. I have another op amp but no voltage ref
And I've still got the dreaded hummmm....
I starting not just to sympathize with Steve but empathize as well.
Anyone got a good recommendation for a scope?
cheers,
-- Andrew
The old scope I use has given up the ghost, I just as I was getting somewhere
100Meg time base delay dual channel irreplaceable.And during my initial experiments a couple of weeks ago I must have taken out either the voltage reference for voltage buffer op amp or the op amp itself. I have another op amp but no voltage ref
And I've still got the dreaded hummmm....
I starting not just to sympathize with Steve but empathize as well.
Anyone got a good recommendation for a scope?
cheers,
-- Andrew