|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Re: 6S45-PE PSE... posted by Brian C. on March 11, 2003 at 04:43:37:
...a good idea but flawed . 6C45 vary enourmously , electrically matched pairs are a must as toroids do not like any DC across them . Toroids working at low HT work very well but any DC caused by imbalance and your circuit is buggered !
Follow Ups:
Koinichiwa,> ...a good idea but flawed . 6C45 vary enourmously ,
> electrically matched pairs are a must as toroids do
> not like any DC across them.Well, the "Semper Musica" 6S45-PE SE Ampliifer has a bias adjustment. If you build the the circuit twice and only derive the "out of phase" drive from the other anode you retain the individual adjustability and hence the amp will have balanced DC.
So I fail to see the flaw. BWTFDIK.
...so your telling me that it's ok to stuff any old 6C45 into a PP amp ? I wouldn't do it , these 6C45 things are all over the place out of the box , best to buy a bunch , burn in then retest and select before using . Same goes for just about any high gm valve . If this pot is between the cathodes , then degenerative feedback will occur anyway and increase Rout , better to select and reduce the value of the pot
Koinichiwa,HAVE YOU ACTUALLY LOOKED at the "Semper Musica" Amplifier circuit? Have you made the effort to draw out what I suggested?
Maybe you really want to have a look at what you are criticising before you criticise.
As for mismatches in PP Amplifiers, note that my proposed circuit has already some deliberate "mismatch" build in to reduce the 3rd harmonic content at the expense of more 2nd Harmonic and a little less power.
It sounds better that way. I would personally tune the Amp for minimised 3rd harmonic content. There is a distinct minima at around 30% Mismatch IIRC after wich 3rd harmonics rise again.
NO NEED TO SHOUT ! Jeez , no wonder you're not flavour of the month round here . I am familiar with the design , I still think this new design is flawed .
Koinichiwa,So, the design is flawed. Fine. If you say so, please explain how.
It is obviously NOT flawed when it comes to DC balance, as both Valves operating points are fully adjustable. So no flaw there, even IF using torroidal mains transformers as outputs. Also, the sub 3k differential drive impedance to the torridal mains transformer abused as output will give good bandwidth.
It is obviously NOT flawed where it comes to AC balance as it CAN be adjusted for optimum balance. Or IF we desire a better overload behaviour and a harmonic spectrum more akin to an SE Amplifier with lower levels of 3rd harmonics than a "theoretically ideal" amplifier we can deliberatly unbalance the Amplifier.
When it comes to noise rejection et al the circuit matches the original "semper musica". Again, no flaw I could note.
As it is in many ways NOT a push-pull amplifier, other than the way the transformer is driven, applying PP logic foes no-where.
So, where is the flaw. Please enlighten me.
Sayonara
PS, may I mention that similar circuits where in use in the 1920's and 1930's with Pentode PP Outputs. They worked then...
I have a decent stock from which to pick matched pairs Nic but it is good that you have pointed this out. When I get around to knocking up a pair of these Pushme-Pullyous I will put results up on my webpage.
Why not use a 350-400V HT supply and stack the things as SRPP cap coupling a mains toroid between the top 6C45 cathode and 0V ? Battery bias with a chunky NiCad or NimH on the cathode of the lower valve . A 230:6-0/6-0 mains toroid with the secondaries in series will provide about a 3k impedence into an 8r load . I suppose there are plenty of possibilities ! That reminds me , I must try building something with the 7788's !
;)
...ooops forgot to add : 6C45 in push pull driving via the cathodes would probably be the best application . Very good damping , should also have low distortion . I'm tempted to try this myself but too busy with sales and other projects at present .
This post is made possible by the generous support of people like you and our sponsors: