mulletchuck
Well-known member
this is for 51X, right?!?!?!?!?!
;D ;D ;D ;D
;D ;D ;D ;D
Group DIY Vari-mu
- Thread starter DaveP
- Start date
Help Support GroupDIY Audio Forum:
The answer "should" be 17V on C2. It is less because C1 and C2 split the voltage for a 9% loss, and D1 adds another 0.6V loss.... 15V is reasonable.
However it then sags further to near 8V, even though the input is _steady_.
You have 17V RMS? Then you "should" have 23.8V as long as the input continues; or maybe 20V with losses. If, with small Decay resistor, it jumps to 20V then drops-off lower (faster than a meter will read), I think this is a problem.
However it then sags further to near 8V, even though the input is _steady_.
You have 17V RMS? Then you "should" have 23.8V as long as the input continues; or maybe 20V with losses. If, with small Decay resistor, it jumps to 20V then drops-off lower (faster than a meter will read), I think this is a problem.
PRR,
There is 17Vrms on each cathode ref ground, so there is 34Vrms across the diodes which is just a simple CT power supply configuration. 0.707 x 34 = 24V. This is not a SIM they are the measurements from an actual circuit.
However, I realise this is only the steady state situation and I need to examine the dynamic reaction to this circuit. I will try square waves and drum beats in the new year.
best
DaveP
There is 17Vrms on each cathode ref ground, so there is 34Vrms across the diodes which is just a simple CT power supply configuration. 0.707 x 34 = 24V. This is not a SIM they are the measurements from an actual circuit.
However, I realise this is only the steady state situation and I need to examine the dynamic reaction to this circuit. I will try square waves and drum beats in the new year.
best
DaveP
I'm having second thoughts about this project, the biggest criticism is it being just another vari-mu.
I've been looking at last years posts on the Collins 23C and 26W, these are completely different animals and from all accounts have a unique sound (Lassoharp are you listening?).
If I made a GroupDIY one those it might be more interesting. Whats the feeling?
Do people think it would still be necessary nowadays to have an output stage to drive half a mile of cable?
I guess it would be called the GroupDIY bridge Compressor?
I'm up for it but I would like a show of hands before taking on such a project.
But if people would prefer another Varimu I am still prepared to make it
happy Christmas everyone
DaveP
I've been looking at last years posts on the Collins 23C and 26W, these are completely different animals and from all accounts have a unique sound (Lassoharp are you listening?).
If I made a GroupDIY one those it might be more interesting. Whats the feeling?
Do people think it would still be necessary nowadays to have an output stage to drive half a mile of cable?
I guess it would be called the GroupDIY bridge Compressor?
I'm up for it but I would like a show of hands before taking on such a project.
But if people would prefer another Varimu I am still prepared to make it
happy Christmas everyone
DaveP
It's all good! Nothing wrong with JAV (just another varimu) limiter.
Collins 26W looks interesting.
That V102 tube modulated by the CV acting as a variable impedance across the coils of the interstage traffo seems unique.
So, hell yeah. Why not?
Personally, I like the heavy metal output amps
Probably makes sense to make them somewhat more lightweight.
But Edcor traffos are cost effective enough to use their 10W 600R outputs
and their psu traffos are not so much more for a little extra juice for bigger output tubes.
So, my show of hands is
W A N T T H E M B O T H !
Cheers
Collins 26W looks interesting.
That V102 tube modulated by the CV acting as a variable impedance across the coils of the interstage traffo seems unique.
So, hell yeah. Why not?
Personally, I like the heavy metal output amps
Probably makes sense to make them somewhat more lightweight.
But Edcor traffos are cost effective enough to use their 10W 600R outputs
and their psu traffos are not so much more for a little extra juice for bigger output tubes.
So, my show of hands is
W A N T T H E M B O T H !
Cheers
kepeb
Well-known member
DAve, I think its great initiative and excellent opportunity to witness the hurdles and workarounds as they come up.
the switch to a collins inspired design is a super idea. but i'll keep following either way.
the switch to a collins inspired design is a super idea. but i'll keep following either way.
ruairioflaherty
Well-known member
Dave,
I really enjoyed your thread on the RCA build. I'll spare everyone the lecture on how things have changed around here but for me I'm all about the learning, I have very little time to build anything. The design discussions with PRR, EMRR and everyone else are where it's at for me. With that in mind I'm happy with whatever you design.
That said others will want a viable project. There are more than enough kits and paint by numbers projects now, I vote for you designing whatever floats your boat and challenges you personally.
Cheers,
Ruairi
I really enjoyed your thread on the RCA build. I'll spare everyone the lecture on how things have changed around here but for me I'm all about the learning, I have very little time to build anything. The design discussions with PRR, EMRR and everyone else are where it's at for me. With that in mind I'm happy with whatever you design.
That said others will want a viable project. There are more than enough kits and paint by numbers projects now, I vote for you designing whatever floats your boat and challenges you personally.
Cheers,
Ruairi
MagnetoSound
Well-known member
I will second what Ruairi just said, to the letter. The learning is the thing for me too. Much of what I am picking up here will be put into use as I find the time, but I am fascinated by the development of this project as it progresses.
Whatever you feel is right for you!
(Just been told off for using the internet on Christmas Day! Quite right too. See you later. 8) )
Whatever you feel is right for you!
(Just been told off for using the internet on Christmas Day! Quite right too. See you later. 8) )
Well I guess 5 good guys is enough for me,
Alan, Ruairi, Dan, Kepeb and Alex,
I will start with the 26W (easier transformers) and get a breadboard prototype working in the new year.
If that works satisfactorily then I will build a working prototype, some parts/approaches may be a bit radical but I will only be satisfied with the same spec although I reserve the right to lower the output to affordable yet pro output levels.
If my attempt fails then I will pursue the vari-mu route.
Have a great holiday
best
DaveP
Alan, Ruairi, Dan, Kepeb and Alex,
I will start with the 26W (easier transformers) and get a breadboard prototype working in the new year.
If that works satisfactorily then I will build a working prototype, some parts/approaches may be a bit radical but I will only be satisfied with the same spec although I reserve the right to lower the output to affordable yet pro output levels.
If my attempt fails then I will pursue the vari-mu route.
Have a great holiday
best
DaveP
Awesome Dave!
The more I look at the 26W the more interesting I find it
Hope you have a great holiday season and thank you so much for the
really interesting build threads and discussions you've contributed.
My pp builds of pentode 660 with hammond sidechain amp transformer,
ba6a style and sta-level style are progressing nicely!
They thank your inputs too
Cheers
The more I look at the 26W the more interesting I find it
Hope you have a great holiday season and thank you so much for the
really interesting build threads and discussions you've contributed.
My pp builds of pentode 660 with hammond sidechain amp transformer,
ba6a style and sta-level style are progressing nicely!
They thank your inputs too
Cheers
vinyvamos
Well-known member
I have been digesting this thread with great interest, and finding it a pity that it never went through to becoming a real and finished unit. It seems that you went over to the 26C bridge topology DaveP, which is another method I want to try at some point. Can I ask if there are any important reasons why you went away from the Heptode vari-mu, using g3 as the control point? I ask because I am about to start experimenting with some 6BE6 tubes, plus I hope to get some 6L7 soon too.
Doug, did you ever manage to scan that 1126C schematic? If so, I would really love to see it.
emrr said:
Doug, did you ever manage to scan that 1126C schematic? If so, I would really love to see it.
Hi Viny,
The project hit a problem with the gain reduction tube.
Basically, the tube was biased -30V I think, and the GR voltage made it more positive, thus lowering its resistance in its position in the bridge.
No matter what I tried, I could not stop it oscillating when the grid got near to 0V. As I didn't want the project to founder so soon after it set sail, I jumped ship to the 26C which worked very well and was recently sold to a Techno DJ who pronounced it "Awesome" (As an Icelander, I hope you appreciate the maritime metaphors) :
DaveP
The project hit a problem with the gain reduction tube.
Basically, the tube was biased -30V I think, and the GR voltage made it more positive, thus lowering its resistance in its position in the bridge.
No matter what I tried, I could not stop it oscillating when the grid got near to 0V. As I didn't want the project to founder so soon after it set sail, I jumped ship to the 26C which worked very well and was recently sold to a Techno DJ who pronounced it "Awesome" (As an Icelander, I hope you appreciate the maritime metaphors) :
DaveP
