Hi-Fi Valve Amplifer Kits

[SpecialK]

Being that I am going to stuck inside for a few more months, I thought I might like to give tube sound a listen.  I don't think I've ever listened to tubes, even my dad's stuff growing up was all solid-state.

So I have a few options.

1 - Restore a vintage piece
2 - Spend $$ for a restored classic
3 - Spend $$$ for some boutique audiophile equipment
4 - Some half-assed product.  Tube headphone amp, pre-amp, or some such thing powered by a wall wart.
5 - Build a kit (gee there's quite a selection of these!)
6 - Scratch build (perhaps a bit more expensive than a kit)

It seems like options 1,2, & 5 costing about the same.  $500 CDN.  Option 5 does seem easiest to obtain.

So, I seek some clarification:

- What type of rectification?  Does this have sonic implications?  I'm leaning toward tube rather than silicon.  Can you still get selenium?
- I've noticed that push-pull doesn't seem to yield a higher power output.  Should I stick with a single ended design?
- What's a reasonable tube complement for sonic vs price? I'm looking at one with 6H8C and EL34B tubes.

I'd like to hear from anyone who's built one of these kits.  More importantly, I would just like to hear from somebody who's a valve enthusiast.



 

[rvalente]

I'd search for a very classic model with plenty available literature and clone the circuit.
Since you've got time, there is nothing more delightful than a nice DIY project.

[bob91343]

Rectification method has no 'sonic' implications.  When tubes are working at their best, they almost equal a good solid state circuit.  Single ended isn't as good as push pull due to the inherent absence of even harmonic distortion in the latter.

I have been active in hifi and stereo for many years, including both tube and semiconductor circuitry.  The biggest lie is that tubes are better.  You may like them better but they reproduce sound material less accurately than good solid state gear.  No exceptions.

You can fall for the various myths such as gold plating, special cables, various brands and colors of tubes, and a whole lot more.  Or you can honestly get a decent amplifier and enjoy it.  Whether tubes or transistor.  Good gear sounds good and you fool yourself if you think that one method of achieving the result is better than some other.

[SpecialK]

I'd search for a very classic model with plenty available literature and clone the circuit.
Since you've got time, there is nothing more delightful than a nice DIY project.

So like any suggestions?  So like a Dynaco ST-35?

[SpecialK]

Rectification method has no 'sonic' implications.  When tubes are working at their best, they almost equal a good solid state circuit.  Single ended isn't as good as push pull due to the inherent absence of even harmonic distortion in the latter.

I have been active in hifi and stereo for many years, including both tube and semiconductor circuitry.  The biggest lie is that tubes are better.  You may like them better but they reproduce sound material less accurately than good solid state gear.  No exceptions.

You can fall for the various myths such as gold plating, special cables, various brands and colors of tubes, and a whole lot more.  Or you can honestly get a decent amplifier and enjoy it.  Whether tubes or transistor.  Good gear sounds good and you fool yourself if you think that one method of achieving the result is better than some other.

I've always believed that SS is better.  I'm not gullible to the audiofool nonsense.  But I am curious to see if I might like a tube setup. 

Really, I would like to run some experiments.  Do tubes sound good?  If so why?  Is it the front end?  Is it the low damping factor and transformer output?  Is it the even harmonics?  The non-flat response?

I'm pretty sure I could run some practical experiments and A-B comparisons.  Might need a couple pair of identical speakers and a pre-amp with multiple outputs. 

[Conrad Hoffman]

Audiophools have forced the price of old tube equipment up beyond all reason. There are some new import builds that are probably OK. I gave up tubes way back for all the common reasons and have never looked back. OTOH, you could always clone a Futterman! http://www.jacmusic.com/techcorner/ARTICLES/English/Harvey-Rosenberg/futterman.htm

[akimpowerscr]

The most important and difficult part to buy in a Hi Fi tube amplifier  is the output transformer.

The sound quality largely depends on this transformer.

If you are doing a tube amplifier project, you should prioritize finding the best possible output transformer.

This generally eliminates all "exotic" projects using tubes that were not intended for audio use.

The following question must therefore be answered: who are the current manufacturers or suppliers of Hi Fi audio output transformers?

Here are some interesting links:

https://www.ringkerntrafo.nl/shop/high-end-audio.html

https://tubedepot.com/

https://www.tube-town.net/ttstore/components-10662/

http://primarywindings.com/?gclid=CjwKCAiA7939BRBMEiwA-hX5J_HMg57sLGIPkHl3LtYl1k4WJ27e8GaocEbebTdgD7l3EJF9cTNtshoCgXcQAvD_BwE

https://www.lundahltransformers.com/products/?gclid=CjwKCAiA7939BRBMEiwA-hX5J9s6ICh_pxky-q_N2WdSsuhkWJEpUqLn41mfCATOPlvPhnjqPIDzSxoCWkIQAvD_BwE

https://sklep.toroidy.pl/en_US/i/Toroidal-Output-Transformers/40

https://www.toroidal-transformer.com/shop/high-end-audio/output-transformers.html

[akimpowerscr]

Regarding power supply,

- it is easier to find a power transformer as they are always made for guitar amplifiers.
Please note, an output transformer for a guitar amplifier is not an Hi Fi output transformer.

- it is preferable to use a soft start or standby system to avoid:
very high inrush current at switch-on due to the charging of the electrolytic capacitors and stress and wear of components by overvoltage when switched on (tubes, capacitors, diodes, ...)

I have an original idea to do this soft start: rectification by rectifier tubes with parallel switching of silicon diodes after a certain delay.

We could also use two separate transformers, one for high voltage, another for filament heating (12 or 24Vac)

The high voltage transformer could be a separation transformer, with secondary, either 115V with voltage doubler, or 230V with bridge rectifier.

Do not use tubes for preamplifiers with low signal levels below 50mV's, only transistors or integrated circuits.

[trobbins]

SpecialK, it seems like you aren't in to electronics testing and faultfinding.  Restoring, or even buying a fully working vintage valve amp and then maintaining it properly may be a step too far, as valves and old parts will fail at some time.  If you can't faultfind all the hums and crackles and 'it just stopped making a sound in the left channel' by yourself it may become an expensive and frustrating path to take, especially if you purchase a well regarded 'hi-fi' valve amp. 

A new valve amp kit may be a good direction to take, but caveat emptor if it doesn't come with a good assembly and test manual, and you will need at least a multimeter and have to do electrical work that has its risks.  Perhaps buying 2 or 3 cheaper kits may get you the chance to A/B compare, and check how golden your ears are, or how biased you become to liking the more expensive amp because it is more expensive or has a more revered part in it.

[rvalente]

I'd search for a very classic model with plenty available literature and clone the circuit.
Since you've got time, there is nothing more delightful than a nice DIY project.

So like any suggestions?  So like a Dynaco ST-35?

Sorry, non suggestion at all, I've no experience with valves or their equipment. I've never wired a valve  more than feeding 6V on the filament just to see it glow ehhehe

Usually, my go-to website for audio reference is Elliot: https://sound-au.com/valves/index.html

[Gyro]

Regarding power supply,

- it is easier to find a power transformer as they are always made for guitar amplifiers.
Please note, an output transformer for a guitar amplifier is not an Hi Fi output transformer.

- it is preferable to use a soft start or standby system to avoid:
very high inrush current at switch-on due to the charging of the electrolytic capacitors and stress and wear of components by overvoltage when switched on (tubes, capacitors, diodes, ...)

I have an original idea to do this soft start: rectification by rectifier tubes with parallel switching of silicon diodes after a certain delay.

We could also use two separate transformers, one for high voltage, another for filament heating (12 or 24Vac)

The high voltage transformer could be a separation transformer, with secondary, either 115V with voltage doubler, or 230V with bridge rectifier.

Do not use tubes for preamplifiers with low signal levels below 50mV's, only transistors or integrated circuits.

A series string of a few common NTC inrush limiter thermistors is a much simpler and more cost-effective method of HT soft start (4 x 20-25R works well). A little bit more heat doesn't matter as long as they are located in the right place.

[akimpowerscr]

I don't like the NTC inrush current protection because it is ineffective or even dangerous.

It suffices to switch the device off and on again shortly afterwards to cause a strong overcurrent and burn the fuse and sometimes even the diodes.

In addition, NTCs constantly operate at high temperatures, which can damage the circuit board and solders.

A component (other than the tubes of course) that operates at high temperature has often a very limited lifespan

[chris_leyson]

^^^

The most important and difficult part to buy in a Hi Fi tube amplifier  is the output transformer.

There are a few technical articles by Peavey on how they biased push pull output stages to operate in one particular spot on the output transformer B/H curve to get a particular sound. Oxford Electrical Products, OEP, make a nice range of tube output transformers, available from RS components. An N35A002F will do for a single ended amplifier and give a few Watts output.

[mag_therm]

Think about getting started  with an old FM mono radio or stereo receiver from late '50's
They are not desired so available at low cost, so no qualms about hacking the circuits.

I modified a Panasonic RE-784, by adding a transformer and silicon diode bridge, to make it safe to work on
and changing all the tubes to 6.3 volt filament.
The output stage (still class A)  was re-done using the same output transformer with a newer speaker,
 and the RF stage/ preselector was improved a bit.
There are other changes I still might do to make its chassis wiring neater, improve the fm demodulator, etc

[SpecialK]

SpecialK, it seems like you aren't in to electronics testing and faultfinding.  Restoring, or even buying a fully working vintage valve amp and then maintaining it properly may be a step too far, as valves and old parts will fail at some time.  If you can't faultfind all the hums and crackles and 'it just stopped making a sound in the left channel' by yourself it may become an expensive and frustrating path to take, especially if you purchase a well regarded 'hi-fi' valve amp. 

I wouldn't say that at all.  I enjoy fixing stuff for sure. 

I'm just not certain as to what I should expect.  Say I fix up an old Fisher 400.  Then I give it a listen and it sounds much like a transistor.  Did I goof or did I succeed? 

[SpecialK]

The most important and difficult part to buy in a Hi Fi tube amplifier  is the output transformer.

The sound quality largely depends on this transformer.

If you are doing a tube amplifier project, you should prioritize finding the best possible output transformer.

This generally eliminates all "exotic" projects using tubes that were not intended for audio use.

The following question must therefore be answered: who are the current manufacturers or suppliers of Hi Fi audio output transformers?

I don't doubt this.  The need for output transformers are one of the biggest disadvantages tubes had versus solid state.  It seems like I would need to buy 3 transformers and a choke and at the low end be in for $200USD.  If I really need to be picky, and start spending significantly more, then this project probably won't fly.

[Pawelr98]

Well, I saved some money by using a switching power supply approach for my experimental tube amps.

Flyback topology is quite useful for generating the high voltage.

I have a bunch of transformers meant for 24V DC power supplies at ~2.5A.
Normally there would be two windings in parallel, each winding beeing actually 2 windings wound together.
So there's a total of 4 windings available. All of the windings used the "safety" thick yellow isolation.

Desoldered the ends, connected them in series, made my own simple UC3845 (3842 is almost the same but starts at higher voltage) driver boards.
It can easily get stable-ish 250V for tube equipment.
With another secondary wound I also managed to get 6V heater, it however lowered the available high voltage down to ~200V.

Flyback is not really a good method to get both the HV and heater voltage.
Such approach is more practical for the 300mA tubes as the heater voltage is higher.
Losses are much lower too, as diode doesn't have to handle multiple amps.
Otherwise I would use two units, one generating HV and second one generating heater voltage.

Made another power supply, IR2153 half-bridge using rewound ATX PSU core.
That thing can put out a lot more power and doesn't require regulation.
270V HV using doubler and 2x6.3V using doubler (for stereo amps the load will be balanced easily).

But I do understand that a lot of tube people don't like such modern approach in the tube gear.
However there are other alternatives out there.

In Poland there's a company making affordable custom transformers (toroidy pl).
Perhaps there's some analog in the Canada as well.
2x50V 60VA toroid costs 61PLN or ~16USD.
Connect the windings in series, use a doubler and you have a nice 250V high voltage.
Then just use a copper wire to wind the heater winding, which is easy for a toroid transformer.
Recommended such approach to quite a lot of budget amp builders over here.

Finding an used 1:1 isolation transformer may be an option as well.


Hi-Fi approach usually means push-pull as distortion cancells out.
Unless you don't actually want hi-fi but the "tube sound" which is actually distortion.
In such case a single-ended approach may be a better way to do it.
Then there's also the feedback, which flattens the response and futher reduces distortion.
However it requires a decent-ish output transformer.
In construction I would put most money toward them, instead of all the other stuff.

[trobbins]

I enjoy fixing stuff for sure. 
I'm just not certain as to what I should expect.  Say I fix up an old Fisher 400.  Then I give it a listen and it sounds much like a transistor.  Did I goof or did I succeed?

A significant issue with restoring or even just checking a supposed 'working' valve amp can be to set them up properly with respect to DC idle voltages and AC voltage gain levels, and to confirm feedback stability, hum, noise floor and harmonic levels and no lurking resonances coming out of the noise floor.  That typically means having a few DMMs, either a modern scope with FFT or a USB soundcard interface setup with probes and software like REW, and test loads.  A normal vintage scope or ears typically can't discern some gremlins.

Not confirming an amp is working properly could easily colour a listening test, just like not setting up A/B levels to be the same.

You may get some awareness from the Audiokarma website.

[Renate]

I would certainly go with modern silicon rectifiers.
No way would I touch selenium!

Then there's also the feedback, which flattens the response and futher reduces distortion.
However it requires a decent-ish output transformer.

One of the earliest amplifiers I had had a selectable tap on the secondary of the output transformer for feedback.
You put it on the same multi impedance tap as the speaker.

[SpecialK]

Usually, my go-to website for audio reference is Elliot: https://sound-au.com/valves/index.html

Some decent information here.  Thanks!

[BrianHG]

1.  A properly designed tube amp will sound almost identical to a properly designed transistor amp, until you reach/exceed the clipping point.  The tube amp softly begins to distort as the transistor amp will heavily sound congested.  Lesson, buy a transistor amp with enough power that you will never run it into the clipping region.

2.  A transistor amp without a DC filter cap on the output usually tends to deal much better with low frequencies, especially with demanding speakers.

3.  Tube amp designs exist which are deliberately designed to add the 'air' effect to the audio.  This is a colorization of the sound unique to some tube amp designs, however, these designs are expensive and usually not too high power.

If you want a serious amp where you cannot argue about the sound quality, I would get this one used:
https://www.canuckaudiomart.com/details/649503254-ocm-500-by-david-belles-mosfet-400-watt-power-house-class-ab/
200watts True RMS/channel.
<3db down, 1Hz to 100KHz. (I measured mine), Flat from 10hz to 50KHz.
@600$ CAD, you cannot beat this one, however, if you want the DIY experience, join https://www.diyaudio.com/ .  You will find both Tube and transistor, class A, & B designs there.  However, just on power supply and caps alone, not even chassis, you will probably pass that 600$ deal I listed above unless you are thinking only ~25 watts/channel.

[Pawelr98]

Then for the power supply there's also a half-diy solution as well.
http://www.qrp4u.de/docs/en/tube_smps/index.htm

Winding an SMPS transformer is easy as only several dozen turns are required, compared to hundreds for mains transformers.

Generally speaking high voltage mains transformers are kind of expensive.
So going around the problem by implementing a switching solution means some great savings.
Also with proper design you can implement lossless soft-start, which is useful for heaters.

As for non-audio tubes.
There are plenty of less popular tubes, that with decent design can provide good performance.

eg.http://www.mif.pg.gda.pl/homepages/jasiu/eka/Sipa30V.html
6S19P triodes, the amp can do 10W at 1% distortion without feedback and 30W at full power with more distortion.
With feedback the amplifier would reach better distortion levels at higher power output as well.
Those tubes are however most likely hard to obtain in the US and Canada, as they were made in USSR only.
Over here those tubes are cheap and rather available.

There are dozens of output tubes, that can be used instead of more expensive audio tubes.
Say EL86, EL82, 6P18P (again, interesting inexpensive USSR audio output pentode).
Even cheap horizontal output tubes can be pushed to have some decent performance at very affordable prices.
eg.http://www.tubes.rs/quality-push-pull-amplifier-pl500-pl504-27gw6-12au7-ecc82-12ax7-ecc83/
Those tubes were made in massive numbers for use in TV's, and can be bought at ~1USD.
PL504 can push about the same power as the way more expensive EL34 or 6L6 tubes.

[SpecialK]

I'm still looking at this.

It has escalated a bit.  It seems that there's a proper(pushpull ultralinear) and a popular misguided(single-ended) way to do this.

It does seem like there is a lot of supply in the market to make this project attainable.  Affordable, not so much.  Hammond seems to make a good selection of output transformers and power supply transformers with all the logical taps. The guitar market seems to have kept tubes in production. I even have a tube shop in town.

I don't see building something like this as good value or particularly practical.  I might build it just to have the experience nad to be able to experience the sound of yesteryear.  If it works out, make it can be  family heirloom.

[SpecialK]

I am about 90% finished building a EL34 ultralinear push-pull.  Took the "easy" route and used a PCB from eBay.  Then spent a tidy sum on some beefy Hammond iron.

I've had the unit up and ran it up to about 30wpc into dummy loads before clipping.  Even after getting the global feedback properly phased, it only takes 0.5Vpk-pk to drive it to clipping.  I haven't set up volume pots yet, but I suspect I might need to reduce the gain or increase the NFB.

I do have some questions about grounding and earthing.  ATM I have the chassis earthed.  While under test I have the unit on an isolation transformer.  However, any stereo receiver I've ever worked on did not have a chassis earth connection despite having a steel chassis.

I have not connected the DC ground to chassis.  Every piece of audio gear I've worked on used the chassis as DC and signal ground.

I suppose I should be using the chassis as both PE and ground.  Does everybody agree?







 

[amyk]

"Hi-Fi" and "Valve" don't go together... people who like the latter want the distortion, people who like the former want nothing more than amplification.