My parallel stereo single ended triode is now ready :)

[Gabe001]

The plans for my triode amp outlined in this thread: https://www.vintage-radio.net/forum/....php?p=1552426
have finally come to fruition. I've completed the build this morning after doing some minor troubleshooting.

Things I've learnt:

1. I won't do this again. It takes an exorbitant amount of iron to get 10 triode watts per channel. If you're sensible build an el84 push pull amp at a quarter of the cost. I've already got the latter and I was curious to see if triodes live up to the hype.

2. the major determinants of THD are the voltage at the ecc82 anodes (the lower the better) and how hard the el34s are flogged (the hotter the better). My el34 valves are running in triode mode at around 23.5w with 465v on the anodes

3. LT spice is remarkably accurate with it's simulations!

4. Why have I not discovered jlcpcb earlier??

The (almost) final circuit is shown in the attached PDF. The only minor change is that the DC supply of the ecc82s was picking up some hum in transit, so I added another stage of RC filtering which is not shown in the pdf. This may not be necessary with a better layout. Also, each diode is rated 1800v (1amp). I'm using my 2 in series for each leg, with snubbers. A 5w 180k resistor discharges the electrolytics. 2 fuses protect the system (hopefully) from diode shorts. The ecc82 heaters have a DC supply with a bridge rectifier each and 2 RC stages of smoothing. There are 2 cl80 thermistors in the transformer primary to limit the switch-on surge (each 47ohms). The mains transformer has very low esr otherwise.

There's no discernable hum with my ear to speaker and except for a very very minor hiss it's completely silent. Max power is 10wpc. Input sensitivity is 800mv RMS. It sounds good to me and there are no stability issues.

Photos of the completed build attached. It's heavy, very very heavy!

Performance figures and plots in next post. Wife has named this amp "DoReMi" as you can see from the label.

[Gabe001]

And here are some performance figures
All measurements done using 20db attenuator using REW/arta on laptop

Thd profile
1w - see picture (remember 20db attenuator) - 0.12% (0.11% second harmonic)
8w - 0.98%
10w (max) 1.6%

Square wave 1khz show in picture (with oscilloscope)
Frequency response shown in picture

[GrimJosef]

Very tidy !

One very small detail, which I don't think got picked up in the earlier thread either: the circuit shows the output valves with g3 connected internally to the cathode. This is true of many octal based tetrodes and pentodes but, unusually, not of the EL34. Mullard chose to bring g3 out separately on base pin 1, alongside the cathode on pin 8, in that case.

I can't quite see from your wiring picture whether you've wired pins 1 and 8 together or not or, indeed, whether you've taken pin 1 to the anode or g2. Given that g2 and the anode are wired together (very nearly) g3 would be sitting in a field-free region if it weren't wired to anything else. So leaving pin 1 disconnected might leave the valve running with something very close to a true triode characteristic.

I'm just curious, that's all.

Cheers,

GJ

[Gabe001]

Thanks GJ. I've got pin 1 and 8 wired together at the valve base. I missed them out once with a single ended el34 ultralinear build and I spent ages trying to figure out why it was distorting much more than expected, so it's the first thing I do now

Also, i need to mention that I haven't done the baseplate and attached the feet yet, but I plan to get those done this weekend.

[Richardgr]

Very nice build!

I could not see the make and models of your transformers, what are they? They are certainly hefty things!

I was wondering if a takeaway of this build would be to put the PSU on a separate chassis?

Edit: Now I see Hammond1627SE in the PDF. But the PSU traffos?

[Gabe001]

The Hammond traffos were just for the simulation in Lt spice.

The OPT is this:
https://a.aliexpress.com/_EHln3Gj. It's rated 25w with2.5k primary and each weighs 2.5kg

The mains traffo is a 7kg monster rated 400w or so. 0-230v primary, 380-0-380, 2× 6.3-0, 3.15-0-315, 70-0, 5-0. It doesn't break a sweat. It's not the quietest transformer I've got but it's very acceptable.
https://a.aliexpress.com/_EykTYYr


The choke is 10u 500mA I cannot find the link but will post if I do

I considered a seperate power supply but I was a but apprehensive of cables carrying 500vdc, and having 6A 6.3v AC running close by radiating god knows what.

[Edward Huggins]

The OP has mentioned how his impressive and lovingly built amp actually sounds.....I have a 300B single ended Stereo amp with no NFB.
Noting the OP's comment No 1 in Post 1, and compared with the Mullard 5-10 Stereo, it sounds easy, with sweet trebles, breathy and with a soft, non-forward, mellifluous bass. This is the kind of sound I grew up with during the War coming from our lovely HMV PX4 Radiogram.

[Gabe001]

Thanks Edward. I'll try to listen to it right after the p-p el84 and report back. Its hard to describe music objectively so maybe I'll upload a video.

Which 300b amp have you got and what speakers do you use with it, if you don't mind me asking?

[Edward Huggins]

It's the AUDION 300B stereo amp and the matching STERLING pre-amp with DYNAUDIO floor standers each with two 7" bass units in each. With "only" 7 watts output per channel, it can play impressively loud if needed. My speakers have a high 91db sensitivity and this helps.

[thermion]

Whats the software you are using there? Looks interesting!

[Diabolical Artificer]

Whats the software you are using there? Looks interesting!

It's Arta & REW

[kalee20]

A good and praiseworthy effort!

Triodes aren't easy to get lots of power out, unless you put lots and lots of power in, but building an all-triode amplifier is one of my aims.

Originally Posted by Gabe001

the major determinants of THD are the voltage at the ecc82 anodes (the lower the better) and how hard the el34s are flogged (the hotter the better).

Now that's curious, I'd have expected the higher the (HT) voltage to be the better, for a given signal swing. As for voltage on the anode itself, I can accept lower voltage being better up to a point, but it depends how that is achieved - raising the load resistance will also raise the output resistance of the stage, hurting high-frequency behaviour (especially driving triodes!); raising anode current would indeed improve things but as it's achieved by reducing bias, there's a point where the stage starts to draw grid current... Voltage distortion may well be low, but the loading on the previous stage will then cause distortion of the waveform on the grid.

Originally Posted by Edward Huggins

I have a 300B single ended Stereo amp with no NFB.
Noting the OP's comment No 1 in Post 1, and compared with the Mullard 5-10 Stereo, it sounds easy, with sweet trebles, breathy and with a soft, non-forward, mellifluous bass.

It's good practice to have not rely on NFB to quash mediocrity! But... I'm wondering how to quantify non-forward mellifluous bass, is it measured in decibels, and relative to what?

Given that a reference level may not be easy to determine, it should still be possible to compare one amplifier design's mellifluity with another (relative mellifluity in db, or maybe a mellifluity coefficient?)... I'd be interested to know how to design for maximum mellifluousness, and after that, how to reverse it so it's definitely non-forward!

[Gabe001]

The software used are arta and rew (room equilisation wizard). Arta can also do fft but I prefer the REW presentation. I use a 20db voltage divider at the input of the soundcard. The soundcard is a USB plug in Behringer uca 202. It's cheap and cheerful and does the job. The software is free.

The effect of the anode voltage on the thd was only seen on the Lt spice simulation (375v Vs around 350v). I didn't experiment with this in practice as I'm happy with the THD numbers. Maybe ltspice isn't simulating this correctly. Happy to share my files if anyone wants to have a go.

[Gabe001]

There have been some comments about triode sound and it's very difficult to describe music objectively.

Just to satisfy my curiosity, and yours, I've recorded some videos.

Same song, same room, same speakers. Filmed with my phone so please forgive the artefacts and some background noise (wife using stapler in the background). The only difference between the two is the amps.

First up is the el84 push pull amp (Armstrong 220 circuit)
https://youtu.be/CatIa0Q8Ass?feature=shared

Next up is the el34 triode
https://youtu.be/17_oVPF-8AI?feature=shared

I'm curious to find out what you think

[Gabe001]

Originally Posted by Edward Huggins

It's the AUDION 300B stereo amp and the matching STERLING pre-amp with DYNAUDIO floor standers each with two 7" bass units in each. With "only" 7 watts output per channel, it can play impressively loud if needed. My speakers have a high 91db sensitivity and this helps.

Thanks ed, I'll look them up. I need to upgrade my mission bookshelfs.

[Diabolical Artificer]

Regarding how amplifiers sound and taking into account the obvious subjectivity, I think a few things can be quantified to a certain degree.

First off is LF response or bass response. I find this aspect of am amps character the hardest to get right. It's either too prominant, too boomy or just not quite right. I've spent quite a while changing coupling caps, cathode bypass caps and what have you. Perfect (to my ears) LF response still eludes me.

Another aspect and easier to get right is the HF response, any half decent OPT will sound ok to our old ears with their built in HF roll off.

Lastly separation, I connect some of my valve amps after listening to my main Yamaha tranny amp, and I can definitely hear a better separation in a music mix, a better soundstage perhaps. There is also a definite better stereo separation with mono blocks.

Finally a lot of the differences I hear between amp A & B disappear after an hour or two, my ears seem to be less optimal over time.

Gabriel's built himself a nice amp, after all the testings done it's the listening test that is definitive.

Andy.

[David G4EBT]

What a superb amplifier Gabriel.

It takes 'home-brew' to a whole new level.

So much thought, care, time and effort has gone into every aspect, and the build quality is exceptional. You mentioned 'why hadn't you discovered JLCPCB 'earlier'?, which, by inference, means that in designing your PCB, you first had to 'discover' Kicad, learn how to use it and to design the PCB. That's so small achievement in itself, as well as getting to grips with LT Spice.

Weight wise, with the OPTs, Mains TX, Choke and hardware, it must be close on 20KG. In old money, that's 3 stones!

I have to confess that to my old ears, in listening to both amps on your YouTube videos, I can't discern any difference between one or the other, but of course, the most important component in an hi-fi system is the most important component is that which no amount of money can buy - a good pair or ears!

[kalee20]

Originally Posted by Gabe001

There have been some comments about triode sound and it's very difficult to describe music objectively.

Just to satisfy my curiosity, and yours, I've recorded some videos.

I've played them (the EL34's are almost red-plating aren't they! When you said you were driving them hard, you weren't joking...)

Both sound good! Playing via an iPhone isn't going to reveal differences I fear.

Triode sound... It's less a question of performance figures and hi-ness of the fi, I feel, and more a question of whether people like the slight colouration that they impart to the signal.

Certainly, and especially with no feedback, the damping on the loudspeaker won't be great. But it'll be better than a pentode or beam tetrode without feedback.

For what it's worth, for my all-triode amplifier (which will be part of an all-triode superhet), I'm intending to use 2 x 3 6J5's in Class A push-pull. Even-order harmonic distortion cancels out of course; odd-order doesn't, but it's no worse than single-ended. I'll wind my own output transformer (probably using strip-wound C cores), this component is far easier for P-P than SE.

Yours... you've built something you wanted to do 'because you can,' and given the topology, you've taken a lot of trouble to optimise it. And then you've built it, so it looks good. Finally, it sounds good! Enjoy...

[theredhouseinn]

You have got a virus in your pdf download.
John.

[Gabe001]

Originally Posted by theredhouseinn

You have got a virus in your pdf download.
John.

There are definitely no viruses in that pdf. You can paste the download URL in virustotal.com and check for yourself.

Re the difference in sound between the amps, I think the el34 sounds "darker" whilst the el84 has more "sparkle". I prefer the former. It's quite subtle though.

Incidentally, the el34s are running 465v at plate with a 620 Ohm resistor. Each draws around 54mA. Cathode voltage is almost 34v, so each dissipates 23w. I can't see any signs of distress in the dark (see pic). Incidentally, B+ to the ecc82 is 355 v.