MagneQuest/Peerless Forum

Welcome! Need support, you got it. Or share you ideas and experiences.

MagneQuest/Peerless Forum

RE: Suggested OPT for GM70?

84.28.82.103

In Reply to: RE: Suggested OPT for GM70? posted by mqracing on June 08, 2008 at 09:12:45

Hi Mikey,

yes I appreciate the difficulty of a design like this, but I have not made up my mind about parafeed yet. Frankly, I have no experience with it but the idea of a capacitor at this position... well.

Is that FS100PS that Gianluca mentioned still available? I could not find much about it on the net. What would the price be for a pair?

Thanks,
Arend-Jan

Follow Ups:

RE: Suggested OPT for GM70? - Paul Joppa 23:02:46 06/11/08 (0)
I worked with Mike when he was developing of the FS-100PF, so I still have an interest in it. (At the time, we - i.e. Bottlehead R&D - thought we were going to try a serious assault on the 845 state of the art. Directions changed, but it was still a technically rewarding project for me!)
The transformer was derived from Mike's FS-100 series feed design. Presumably that one is still in the archives, though you might have to twist Mike's arm pretty hard to get some made. :^) It's quite a good design in its own right. If you want to do series feed without capacitors, all you need is a good shunt regulator at the end of the power supply - see the late John Camille's articles in Sound Practices for more on this. Combined with fixed bias, the signal current loop includes only the shunt regulator, tube, and load - no capacitors. (Note that the same analysis applies to a transformer-coupled driver.) The shunt regulator must carry at least as much current as the tube it is regulating, so it can create at least twice the heat. This inefficiency, along with the large transformer size required to carry both AC and DC, are the arguments against series feed - as Mike says, if it is done right it can sound as good as anything else done right.
Parallel feed does two things. First, it isolates the power supply from the signal current loop. This isolation is through the plate choke inductance, so it is most effective at mid and high frequencies; we have found that a shunt regulated power supply still improves the sonics, but the regulator does not need to carry the full current, and even with no regulator the sound has most of the benefits of a shunt regulated series feed arrangement.
Second, parallel feed allows the transformer to be smaller since it does not carry DC. The FS-100PF has a shorter stack even though its power handling capability is substantially larger than the FS-100 series feed. The shorter stack reduces parasitic capacitance and leakage inductance; between us Mike and I came up with a revised winding schedule that took full advantage of this. This included some design principles and strategies we acquired by studying Mike's Peerless archives. I learned a huge amount from this exercise, and I will be forever grateful to Mike for giving me the opportunity to participate in this adventure.
Parallel feed does have a capacitor in the signal current loop. For a top-line setup with a 10K load, I would hope for 100 henries of plate choke, calling for about a 2uF capacitor, rated for something like 1.5 times the plate voltage. At GM-70 voltages, that's quite a large capacitor, but it is much smaller than a power supply capacitor and hence one might be able to get a better performing unit.
I know that was a pretty long and complex post, I hope it is helpful. I'll be out of town for the next week or two, but happy to continue this discussion when I get back if anyone is interested.

Edits: 06/12/08
RE: Suggested OPT for GM70? - mqracing 08:18:17 06/11/08 (11)
Hi AJ:
you wrote in part;
::::I have no experience with it but the idea of a capacitor at this position... well.::::
awe.... spooked by a cap.... but consider... that in a series fed arrangement you will have a capacitor in the signal path (the last cap in your power supply is in the ac signal path)--- and likely that it will be much larger in value than the parafeed cap. So in either case you will have a capacitor in the signal path.

:::Is that FS100PS that Gianluca mentioned still available? I could not find much about it on the net.:::
The FS-100PF was a parallel feed output transformer.
MSL

Builder of MagneQuest™ & Peerless™ transformers since 1989

Edits: 06/11/08
- RE: Suggested OPT for GM70? - arend-jan 09:00:00 06/11/08 (10)
  awe.... spooked by a cap.... but consider... that in a series fed arrangement you will have a capacitor in the signal path (the last cap in your power supply is in the ac signal path)--- and likely that it will be much larger in value than the parafeed cap. So in either case you will have a capacitor in the signal path.
  Yes I'm well aware of this, with SE you cannot lose the cap. And your argument is valid (but to be frank I find it uncalled for to say something like 'awe ... spooked by a cap'). Like I said, I have no (first hand) experience with it. That is my concern.
  Not too unreasonable I think if you're going to spend a lot of money on an OPT with the possibility that you don't like the sound of the design topology.
  The FS-100PF was a parallel feed output transformer
  Can I understand correctly that it is no longer available?
  
  OK, so let's assume I'm willing to go parafeed. What are the options and prices?
  Thanks.
  
  Edits: 06/11/08
  - Hi Mike..did you not have one or two extra fs-100pf's - Bas Horneman 11:59:10 06/11/08 (7)
    you just had to wind some chokes for them.
    
    I can lend Arend my fs-100pf's and if he likes them he could maybe order the one's you had left over.
    To infinity and beyond!!!
    - BAAAAS! - gluca 13:58:30 06/11/08 (4)
      Should I understand you are not using those copper GM70s I sent you?! C´mon I sent them one year ago! What have been doing all these months?
      
      :-)
      - Mmm I only got them in october 2007 so that is 9 months ago - Bas Horneman 15:38:20 06/11/08 (0)
        
        In Reply to: RE: BAAAAS! posted by gluca on June 11, 2008 at 13:58:30
        
        and who said that I was going to build something? I just collect MQ Iron because I like having it...it makes me feel rich. And I age anneal my iron for a least a decade. ;)
        To infinity and beyond!!!
      - RE: BAAAAS! - arend-jan 14:01:53 06/11/08 (2)
        
        In Reply to: RE: BAAAAS! posted by gluca on June 11, 2008 at 13:58:30
        
        OK I heard enough!
        
        Bas, I hereby summon your copper GM70 and FS100PF. Name your price :-D
        
        Hi Arend...not for sale ....but you can "run them in" for me - Bas Horneman 15:26:24 06/11/08 (1)
        
        In Reply to: RE: BAAAAS! posted by arend-jan on June 11, 2008 at 14:01:53
        
        if you like :-)
        To infinity and beyond!!!
        
        RE: Hi Arend...not for sale ....but you can "run them in" for me - arend-jan 00:12:01 06/12/08 (0)
        
        In Reply to: RE: Hi Arend...not for sale ....but you can "run them in" for me posted by Bas Horneman on June 11, 2008 at 15:26:24
        
        Appreciate the offer Bas, really nice.
        
        Let me see if they still need breaking in when I'm actually in a position to use them (e.g. I'm still in the sourcing parts stage, obviously).
        
        Thanks again!
    - RE: Hi Mike..did you not have one or two extra fs-100pf's - mqracing 12:08:58 06/11/08 (1)
      Hi Bas:
      
      I do have two pairs left... but they are on hold for a customer in Canada.
      
      How sweet of you to offer a loan to AJ.
      
      Interestingly--- I was halfway smitten by the airgapped design that I penned just a few evenings ago for the operating points that AJ mentioned. It's a bit short (in my estimation) in L--- iirc, I calculated 43H. Not terrible--- I had calculated the power response to be 3db down at something like 26 or 27 hertz.
      
      And then you can do silly things (smile here) like putting huge 50 to 75 mfd caps in the ultrapath\WE arrangement so that you can avoid (smiles here as well) that darn pf cap of four to six mfds.
      
      For parafeed--- I would encourage AJ to perhaps adjust his operating voltages and currents to make them dovetail into the 5K impedance of
      the EXO-050.
      
      Bas someday we have to meet up.
      
      MSL
      
      Builder of MagneQuest™ & Peerless™ transformers since 1989
      - Hi Mike, would be great to meet up..maybe - Bas Horneman 00:42:36 06/13/08 (0)
        
        In Reply to: RE: Hi Mike..did you not have one or two extra fs-100pf's posted by mqracing on June 11, 2008 at 12:08:58
        
        at vsac some time in the future....
        To infinity and beyond!!!
  - RE: Suggested OPT for GM70? - mqracing 10:20:03 06/11/08 (1)
    Hi AJ:
    you wrote:
    
    :::Yes I'm well aware of this, with SE you cannot lose the cap. And your argument is valid (but to be frank I find it uncalled for to say something like 'awe ... spooked by a cap').:::
    I actually intended the "awe.... spooked by a cap" in a playful, tongue-in-cheek manner. Apologies for the offense you found in the expression. I had no intent to offend at all.
    However, I could soapbox this--- another term I've used in the past is
    "capacitoritis"--- transformers have tons of little "hidden" capacitors in them. Resistors have inductance. Capacitors have resistance (very little) as well as some inductances in them.
    R,L, and C are the three basic building blocks of electronics. I don't find any one of them to be "evil", "undesirable", "sub-optimum" or etc in-and-of-themselves (generis).
    Hence--- I sometimes picture the "age of innocence" wherein someone ascribes a valuation to one of these building blocks--- sort of in an "innocent" manner--- perhaps reflecting an erroneous view based on a prevailing attitude or viewpoint that itself tends to be transitory over time. Go back some years and the moreso dominant view was to eliminate from the signal path whenever and wherever possible transformers themselves --- for all the "evils" that allegedly they embodied. So, over time--- these notions come and go.
    
    I find it more useful to carefully study and recognize the roles and\or functions that each of these building blocks (R, L, & C) can bring to the enterprise.
    
    So, again--- I was not pointing to you personally--- with my intended tongue-in-cheek response but rather I was trying to address (for the umpteenth time) the mistaken notion that only parafeed has a capacitor in the signal path.
    But, I'm probably getting in even deeper--- so at the risk of offending any further--- please accept that what I said was meant good naturedly.
    
    :::Not too unreasonable I think if you're going to spend a lot of money on an OPT with the possibility that you don't like the sound of the design topology.:::
    Again--- if I may--- take for example SRPP (or pick any other "topology")--- was real popular at one point (say early nineties based on some articles in SP)--- then became unpopular--- sort of like dresses go in and out of style--- my take on topologies is that most (if not all) can be done well or done poorly. Part of is in the designers understanding of the topology, the selection of parts, the selection of layout, the selection of specific operating points--- along with any hunches or insights that the designer\builder may bring to the table. I've heard SRPP arrangements that were quite good--- and some that were quite poor sounding.
    Same goes for parafeed vs series feed. Each can be done well. On paper PF offers a host of technical advantages IMO. However, this does not mean you cannot build a great sounding series fed SE amp.
    Making choices--- btwn series feed and parafeed--- as well as two thousand and four hundred and twelve different circuit topologies that could be implemented--- can be paralyzing--- and I don't have any sure fire way to narrow this down a whole lot myself--- other than gaining your own listening experiences over a period of time.
    I can feel the water up to my chin now--- but all of this (what I am writing) is meant to be liberating---- to open or expand horizons not shut down or limit choices.
    If you have an interest in learning more about PF-- check out many of the posts on this forum as well as Bottleheads. If you want to appeal to published reviews--- check out many of the positive glowing reviews of sevral of the PF amps that Gordon Rankin has built over the years.
    Again--- with the optimization of design, materials, and layout--- there can be many paths to musical nirvana (from a particular subject's POV).
    
    ::::The FS-100PF was a parallel feed output transformer
    Can I understand correctly that it is no longer available?:::::
    correct. It was built as a limited edition transformer and has been sold out for quite some time.
    
    :::OK, so let's assume I'm willing to go parafeed. What are the options and prices?:::
    
    If your willing to adjust\optimize your operating points for the EXO-050 output trans--- Jim Dowdy uses this PF output in his GM 70 amps. But it has a five K primary impedance---- and hence you might have to adjust your tubes operating parameters to make for a good match.
    Otherwise--- I thought I said in my first response to you--- that I had (on my own) done a fresh design at your operating points---- 7,000 ohms and 100 madc as an conventional airgapped series fed output transformer.
    And overall I liked what I saw on paper. As a rough estimate--- as a custom ouptut--- given it's size and complexity and the materials I would use--- I would estimate that these would cost about $750 a pair.
    For info on our EXO-050 please refer to our catalog at
    www.magnequest.us
    
    thanks Arend Jam--- if I've managed to pee-O you even further then send me an email and I would be happy to call you and smooth things over---- I've seen you post on the Asylum for a long time--- and actually have always had a good vibe about you personally. So none of this was or is intended to be rude or impolite.
    
    MSL
    
    Builder of MagneQuest™ & Peerless™ transformers since 1989
    
    Edits: 06/11/08 06/11/08
    - RE: Suggested OPT for GM70? - arend-jan 14:00:44 06/11/08 (0)
      Hi Mickey,
      
      No problem. Apparently I misinterpreted your statement, electronic correspondence tends to do that sometimes. Let's not waste too many words on it.
      
      Actually, I agree on your observation of fashion trends, yet noone is immune to it. You should be glad transformers are in fashion these days :-p
      
      My current design looks like a 1G4GT with CCS load (gary pimm) coupled to a 45 followed by a 1:1 interstage to the GM70. GM70 with fixed bias.
      
      The EXO-050 I'm not sure of. I'd rather go up to 10K than down to 5K. Also power handeling is a tad tight with 20W (don't know at what frequency, 20Hz?)
      
      I think a custom tranny would be the way to go, or I could give that FS-100PF a go and see how I like the parafeed arrangement. How about a parafeed autoformer? Can you see any advantages there?
      
      Lot's to ponder on.
      
      Thanks for your elaborate response.
      
      Regards,
      Arend-Jan

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.