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    Building, troubleshooting and testing of these amplifiers should only be
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Parafeed 45 amps

I have an usual amount of experience with amps like this. Kurt's is pretty straight forward. The only change I would make is to replace the zener diode and cap in the current source with a 33K resistor in parallel with a 10,000uF/6V cap. (not originally my idea, this came from a very experienced designer)

Without spending a lot of extra money, a pair of 0D3's in series would give you a regulated voltage supply for your driver, allowing you to control the potential voltage across the MJE-350.

I don't like Pimm's amp at all (no offense Gary). Current sources like compliance, and going monkey feed means that you are giving up driver headroom. On the output stage, I would use the MJE5731AG in place of the MJE-350. If you found a suitable plate choke, you could maintain the topology and use a choke loaded driver instead of a CCS'd driver, and you'd have a nice piece of kit!

IMO, a completely shunt regulated amp will outperform either of these.

-PB
 
Do you have a schematic you could point me to? I'm using about 95db efficient speakers and I don't listen to loud music, so I thought 2-3 watts might be enough. I keep reading about the DHTs and I thought if I'm going to build a replacement amp at some point, I might as well build one I don't need to replace any time soon, if ever. The 26, 10Y and 45 seem to have a consistently good reputation.
 

45

Member
2008-12-18 2:29 am
UK
Do you have a schematic you could point me to? I'm using about 95db efficient speakers and I don't listen to loud music, so I thought 2-3 watts might be enough. I keep reading about the DHTs and I thought if I'm going to build a replacement amp at some point, I might as well build one I don't need to replace any time soon, if ever. The 26, 10Y and 45 seem to have a consistently good reputation.

You might also evaluate if buying an OT without gap + Choke + a really good capacitor is better than a properly good SE OT. Using a CCS you get better noise rejection given the same PSU but you can always design a better power supply. I don't remember MagneQuest products to be cheap....
Many years ago parafeed was more common not only to save money but also because of poor quality of magnetic materials which couldn't give satisfactory perfomance in some applications. The latter is surely not your case as you are going to use small power devices. I don't think the 26 will give enough power.
You might also consider the 4P1L in triode connection which is quite linear and very cheap! Then you could invest the money you save in good SE irons and PSU.
 
The only thing I think I'm sure of is that I'd like to build a single ended tube amplifier using excellent tubes and iron, and generating "just enough" watts to give me good dynamic range at listenable levels. I have tinnitus and I can't listen to very loud music. I measured with an app on my iPhone once and somewhere around 94dB was my max limit, though I'm sure some of the peaks were beyond that. I'm pretty sure 2 watts will be good enough, and from all the raving I've read about it the 45 seems like a great output tube. I don't yet know enough about design to intelligently comment, and I haven't heard these things because I don't know the right people, apparently. I'd be happy to try the plain old transformer coupled output, it will probably be the easiest thing to do anyway. The driver I suppose could be anything, but I've read a few posts about the 26/45 combination being excellent. Isn't the Wavelength design an SRPP? As far as I understand, that uses a push-pull driver arrangement with the output tube as a single ended follower. Doesn't that defeat some of the purity of a single-ended design? It looks like Kevin Kennedy has a very similar design, maybe a bit simpler:

http://www.kta-hifi.net/projects/amp_page/45dht/45_dht_all.pdf

Looks like Gordon Rankin uses parafeed output for his production 45 amplifiers, probably with SRPP drivers? Bottlehead uses it too. There just seem to be a bunch of examples out there, so there must be something to it.. I dunno.
 

45

Member
2008-12-18 2:29 am
UK
The only thing I think I'm sure of is that I'd like to build a single ended tube amplifier using excellent tubes and iron, and generating "just enough" watts to give me good dynamic range at listenable levels.

You don't need spend a fortune to get excellent results. The Tamura F-475 is just so right for the 45 (and 4P1L I would say). It also has the additional bonus of holding its value as this is really a time proven performer. To get really marginal improvements in 1-2 areas you need to spend 3-5 times more.....
 
26/45 amp

Ok, in how many ways would this be a disaster? It's just the CCS loaded driver stage from Gary Pimm's design, with the filament supplies replaced with Rod Coleman's design - stolen from the 26 preamp thread, and from various other posts. The output is simple single ended transformer, but could just as well use the parafeed output from Kurt Strain's design by swapping the air gapped transformer for a parafeed, and adding back in the choke and capacitor. I don't have TubeCAD or anything, I'm just trying to get an idea of whether this is total crap or might sound good...
 

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mp9

Member
2006-06-07 7:00 am
Looks like Gordon Rankin uses parafeed output for his production 45 amplifiers, probably with SRPP drivers? Bottlehead uses it too. There just seem to be a bunch of examples out there, so there must be something to it.. I dunno.
...small group, Gordon seems to be doing the most of a seemingly rare bird. I can't think of to many more in or out of production -
Yamamoto A-08 S
Fi 45, Fi X45 (Fi X4, 46 tube, interesting)
Audio Note Paladin
Jeff Korneff 45
Electra-Print Audio 45 Silver Stereo Amp
Wellbourne DRD 45
Cary CAD45 SE
J.C. Verdier SE 45
James Burgess 45

Interestingly, i've read of Gordon R's dislike of the 2A3 tube and although i'm finding i prefer the 45, would seem not all feel the same, least not commercially. Will say the higher level AN 2A3 amps i've heard were pretty impressive too (food for thought) -
Yamamoto A-011
AudioNote Souga (Kondo)
AudioNote Neiro
AudioNote Baransu
AudioNote Kageki
AudioNote Vindicator
Fi 2A3 monos, Fi X2a3
Sun Audio SV2A3
 
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Ok, in how many ways would this be a disaster? It's just the CCS loaded driver stage from Gary Pimm's design, with the filament supplies replaced with Rod Coleman's design - stolen from the 26 preamp thread, and from various other posts.


Pimm forces the 45 to start slowly, delaying B+ application and thusly voltage to the driver tube. There isn't any whacky startup behavior in this manner, and from this standpoint the design has good functionality

When you pull the CCS off the cathode of the output tube, the 26 and the 45 may have uneven warmup times, potentially leading to arcing in the 45. (Also, that CCS would have pretty heavy LED bias with a 75K resistor on 45 plate voltage, I'd go with 150K)

The Magnequest RH output transformers were a good suggestion.