SET amp owners thread

[geetee1972]

nice setup. I see the amps are in camouflage colors to blend in with the plants !

View attachment 138666

Here is my "old timer" Silvercore amp. They also made a 300B version of this (essentially the same but with 300Bs instead of 2A3s). Lots of iron and weighs over 30Kg...for a 3.5watt amp!

I like the retro look! They still make a 300B amp don't they? I lisetended to one when I was making the original purchase but preferred the extra saturation of the 833.

 

[morricab]

I like the retro look! They still make a 300B amp don't they? I lisetended to one when I was making the original purchase but preferred the extra saturation of the 833.

Only as DIY and it is no longer interstage transformer coupled, so I expect that my amp actually sounds better. They used to make commercial 300B monos that might have been interstage design but i can't find any info about them.

 

[christensenleif@msn.com]

 

[Atmasphere]

So yes, 'education' is why I'm here:

View attachment 138686

The use of a pentode in pentode mode while driving a 300b is problematic due to high distortion and high output impedance of the pentode. I'm sure it will play, but it can do better. You need a bit of current to drive a 300b properly which is why power tubes are often tapped for the job. The EF37 OTOH has exceptional characteristics in triode mode; if the gain of a pentode is desired I suggest feedback between the plate of the tube and its grid to correct for the excessive distortion for which pentodes are known. You can do this and still have plenty of gain and get very good sound; take a look at the technique in this leak point one schematic which is a very musical preamp.

The advantage of doing feedback in this manner is the feedback does not get distorted by the tube before being able to do its job (unlike when applied to the cathode!). So you get far less of the audible problems which has given feedback a bad rap. If its not obvious from the schematic, to use feedback in this manner a resistance in series with the signal is required in the grid circuit. The feedback is mixed with the signal in the same manner as done with opamps. The ratio between the two resistors determines the gain.

The 470K grid grid resistor for the 300b is on the high side. 250K is the maximum recommended for a 300b in this application ('cathode' or 'self' bias). I suspect a Voltage drop will occur in it which will alter the operating point of the tube. Since the tube is meant to be cathode biased, the correct grid resistance should be observed! This will mean the coupling cap value will have to be increased to maintain the same timing constant, which is -3dB at about 3.5Hz. This value was probably chosen since the output transformer is likely not capable of full power below about 35Hz. The 3.5Hz frequency thus chosen to prevent phase shift from robbing the presentation above that frequency of any impact (the effect of phase shift in the lows robs impact just so you know). So the coupling cap used between the driver tube and 300b should be increased to 0.15uf or 0.22uf to work with the correct grid resistor value.

I recommend an additional tube as a driver for the 300b. Since a B- supply isn't in the cards a 6SN7 or 6BL7 could be used as a plate follower- if it were me I'd parallel the tube sections so as to allow for more plate current to drive the grid of the 300b. The coupling cap C7 can be the same value, between the EF37 and driver tube. A 470K grid resistance will work fine with a 6SN7 with sections in parallel. If you need further resistance values for the plate load and cathode of the 6SN7 let me know.

 

[Atmasphere]

2cents incoming ,

Never heard an OTL sound better than a SET , thought i would prefer the OTL from a design point of view but in reality not .

SET’s are like a Giant enigma, when impedance and drive match the sound is really top tier , music dependent also for sure , favoring and best on classical music and natural acoustic instruments vs multi track studio Recordings ..

+1
This is exactly right!! I can't speak for most OTLs, which tend to use feedback; ours don't. As a result ours are very load sensitive so to get the best out of them the right speaker must be used. Anyone getting the best out of an SET has faced the same issue. Zero feedback is the issue here- it means the amp, whether OTL, SET or PP is sensitive to the load. So the most successful systems will be using high efficiency, low phase angles in the crossovers (if there are crossovers) and likely the designer of the speakers used a tube amp as reference.

 

[bonzo75]

+1
This is exactly right!! I can't speak for most OTLs, which tend to use feedback; ours don't. As a result ours are very load sensitive so to get the best out of them the right speaker must be used. Anyone getting the best out of an SET has faced the same issue. Zero feedback is the issue here- it means the amp, whether OTL, SET or PP is sensitive to the load. So the most successful systems will be using high efficiency, low phase angles in the crossovers (if there are crossovers) and likely the designer of the speakers used a tube amp as reference.

So who said that SETs are universal for speakers? They only work on carefully selected speakers suited for SETs

 

[DasguteOhr]

View attachment 138686

If you want to use a 5r4 tube rectifier, the first charging capacitor C1 must be significantly smaller (max. 4uf tube specification) or a series resistor must be used(the b version is rated max 20uf). Otherwise you will not be able to enjoy your tube rectifier for long. If you need the maximum current, the choke must not be larger than 5 Henry. After the choke you can easily use 2x 47uf (good quality). Ralph explained the rest very well. I would determine the perfect size of the coupling capacitor C 7 with a squarewave measurement. Too large ones make the amplifier slow (charging and discharging times are determined by the anode resistor driver R4 and grid leakage resistor R7 of the 300b.

P.S or a gz 34 is rated max 60uf

 

[Lagonda]

I´ve swallowed and left a trail of camel carcasses in my path in the persuit of better sound
the biggest of them all was using Powersoft modules on both FLH from 550 and down
2kw on the subhorns and 1kw on each JBL 2220B, all with individual dsp......
the transition between 300Bs and the Powersoft is perfect and I had to tell people who visited what I had done, and they refused to believe it.....

Still trying to find a fitting model of that particular camel myself, the Italien amp-maker you suggested is definitely not an option. I think he has been out of business since 2022. No post on facebook, no response to emails, and his website was down for 3-4 month this year.

 

[christensenleif@msn.com]

Powersoft.com

 

[Lagonda]

Powersoft.com

I thought Powersoft only sold directly to manufacturers ? You gave me this link a while ago, https://www.rougeaudiodesign.com/en/studio-n-12
he seems to be out of business.

 

[christensenleif@msn.com]

They sell complete amps

 

[Lagonda]

They sell complete amps

I will try directly to Powersoft, thank you Leif.

 

[christensenleif@msn.com]

I was lucky enough to get a pair of Litemod 4hv

 

[Audiohertz2]

Yes those same ones, well in green at any rate. The hammerton finish is something I will claim credit for. I asked if mine could be finished in hammertone green, which wasn't something Christoph had done before. I got the idea from the Leica MP Hammertone (I don't own one) and wanted them to match my room:

Home by Greg Turner, on Flickr

Home by Greg Turner, on Flickr

hORNS FP15s, Silvercore 833MKII by Greg Turner, on Flickr

Wow painted his room to match the amplifiers ..!


Wicked .....,

 

[PeterA]

The next problem is SETs really can't make bass.

 

[Atmasphere]

So who said that SETs are universal for speakers? They only work on carefully selected speakers suited for SETs

+1
So you know how one of the more common comments you read about SETs is how dynamic they are for their low power? That is what happens when you play them on a speaker that isn't efficient enough for the amp.

When you get over about 20-25% of full power, the higher ordered harmonics that the ear uses to sense sound pressure show up on musical transients. So the ear interprets that as 'dynamic'. This is why I say you really only have 20-25% usable power as above that level with most SETs the distortion imparts that dynamic quality. Its fun, but its not true to the recording.

So to answer your question, 'Anyone who says their SET is more dynamic than other amplifier types.' Real dynamic contrast comes from the signal, not the amp.

FWIW Dept.: A string bass only goes to 40Hz and most of what you hear of it is the 2nd harmonic. For this reason a lot of bass cabinets really don't go down much below 80Hz. I started playing bass in 6th grade and still do...

Perhaps when I say 'won't play bass' I'm not being clear. When I played in the orchestras there were usually fairly large bass drums, which had output closer to 25Hz. I like to be convinced about the bass region (and play a lot of electronic music that has deep bass) so when I say 'won't play bass' I mean the bottom octave. Here's another example:
Organ symphony try it at 10:00

That organ has pedal tones to 16 Hz and they are on the LP. If your system plays them properly stuff will shake.

 

[bonzo75]

+1
So you know how one of the more common comments you read about SETs is how dynamic they are for their low power? That is what happens when you play them on a speaker that isn't efficient enough for the amp.

When you get over about 20-25% of full power, the higher ordered harmonics that the ear uses to sense sound pressure show up on musical transients. So the ear interprets that as 'dynamic'. This is why I say you really only have 20-25% usable power as above that level with most SETs the distortion imparts that dynamic quality. Its fun, but its not true to the recording.

So to answer your question, 'Anyone who says their SET is more dynamic than other amplifier types.' Real dynamic contrast comes from the signal, not the amp.


FWIW Dept.: A string bass only goes to 40Hz and most of what you hear of it is the 2nd harmonic. For this reason a lot of bass cabinets really don't go down much below 80Hz. I started playing bass in 6th grade and still do...

Perhaps when I say 'won't play bass' I'm not being clear. When I played in the orchestras there were usually fairly large bass drums, which had output closer to 25Hz. I like to be convinced about the bass region (and play a lot of electronic music that has deep bass) so when I say 'won't play bass' I mean the bottom octave. Here's another example:
Organ symphony try it at 10:00

That organ has pedal tones to 16 Hz and they are on the LP. If your system plays them properly stuff will shake.

Sorry your arguments are too straw man for me

 

[Atmasphere]

Sorry your arguments are too straw man for me

A strawman is when the argument isn't addressed- a different one is addressed and knocked down instead. The result it like any logical fallacy, inherently false.

So what was I not addressing?

 

[Kingrex]

A strawman is when the argument isn't addressed- a different one is addressed and knocked down instead. The result it like any logical fallacy, inherently false.

So what was I not addressing?

Thougt that was a scarecrow

 

[the sound of Tao]

So yes, 'education' is why I'm here:

Atmasphere,
This is a SET appreciation thread, if you don’t appreciate SET amps how can you ‘educate’ us??

Taking the roll as teacher in a subject that you clearly don’t believe in is wrong.

Beyond this you have a very significant commercial interest and potential for financial gain from disparaging SET amplifiers that compete directly with your products in the marketplace.

To teach in a subject that you have a clear conflict of interest in is fundamentally unethical.

I have taught full time for the last 20 years and as a qualified educator can only suggest you are completely off course in taking over a lead educator role in this particular thread.