Changing tubes on a single ended amp

[BigElectricCat]

Hi guys,

I'm looking at getting the VHT Special 6. It is described as a single ended amp. I'm not sure what that means but I am assuming it means there is only 1 power tube?

The internet is full of talk of folks changing this tube and that tube and the stock tubes being rubbish.

The internet is a dangerous place! I have also seen threads where people talk about changing the neck, bridge, tuners, and trem system of expensive guitars before they consider them fit for the purpose.

Will changing the tubes in a small amp like the Special 6 make a big, noticeable, audible difference? Is it likely to be worth the money?

Also, can I change the tubes myself? I'm told there is no need to make any modifications to the circuit or perform biasing when changing tubes. I know next to nothing about electricity, can I safely do the job on my own?

Cheers,

Tony

P.S

It's been a bit quiet around here recently, hasn't it?

[Gary_W]

Single ended does mean that there is only one power amp tube (valve - we call them valves in the UK but the terms are interchangeable)

I don't have the amp you mention but I do have an amp with only one power tube. The manufacturer of my amp designed it to work with several different power valves so I can take the sound in different directions. The different kinds do indeed give different flavours. The differences can be fairly major or pretty subtle depending on what you are going from / to. HOWEVER the bigger influence on the overall sound of the amp is the overall amp design and the speaker / speaker cabinet you run it through - speaker choice and the size / style of the cabinet makes a vast difference.

I changed my power amp tube from a C6A7 to a Gold Lion KT77.... These two mentioned are 'compatible' with EL34.... All are slightly different flavours of valves that are often found in amps that give the 'British' sound - think Marshall cranked up. 6L6's are more typically assosciated with the 'American' sound (eg Fender). I can apparently use 6L6's in my amp too without any problem but I've never done so - I love the way it sounds now.

I've also recently changed the preamp valves (12ax7's) from the stock JJ's to one gold lion and one Tung Sol. For a couple of days, the sound was much, much brighter and the overall volume of the amp went down considerably. Now they have been played for a few hours, it's settled down - the volume of the amp is back to normal and, whilst these are 'topier' than the old jj's they have rounded off and mellowed to a rather wonderful sound. I wouldn't have believed how much they changed over the first few days but they absolutely did!

IMO, the changes have been an improvement but the thing is that valves are a bit of a dark art - the sound of a valve changes over time and some of the improvements I got might have just been because the old ones were getting a bit old and tired or it may be that the more expensive ones sound better purely because (physchologically) I believe they should because they are more expensive! There are differences between valve types but unfortunately these differences vary depending on the amp and are subjected to your ears on the day. The final link in the chain is that the web gives an awful lot of snake oil so you really just need to try and live with your existing amp then trust your ears without all the Internet chatter!

Some folks out there will insist that nothing will do unless it's a 1960's Mullard that they found in a cupboard under the stairs in the house of a virgin who rides a unicorn.

Part of the problem here is you can never prove them wrong - they have that valve, you don't. You imagine it to be fab because it's old, expensive and rare. This could well make it the best valve ever. It could also make it old and tired, but the person who has just spent that kind of cash on it is hardly going to admit that to themself or anyone else. Be assured that there will be a 'standard' valve out there that will make you smile and it might even be the bulk standard ones that come with the VHT.

This little 7 watt amp I have here makes me smile every time I plug it in. The sounds it makes (to my ears, needs and tastes) blows any amp modeller I've heard out of the water and I absolutely love it. All of the valves in there are current production models. That'll do for me. Yours and everyone elses opionion will vary and all such opinions are equally valid

My advice really would be to get the amp and use it extensively before you chop and change valves. Because tonal quality of an amp is based largely on personal perception, you may find you're quite happy with the VHT out of the box. If you do want to change things, ensure you only use recommended valve types and when you change, ensure the amp is off and the tubes are cold (i.e. don't play it for half an hour and then change them as they get very hot!)

Gary

[CaptainChoptastic]

My advice really would be to get the amp and use it extensively before you chop and change valves. Because tonal quality of an amp is based largely on personal perception, you may find you're quite happy with the VHT out of the box. If you do want to change things, ensure you only use recommended valve types and when you change, ensure the amp is off and the tubes are cold (i.e. don't play it for half an hour and then change them as they get very hot!)
Gary

Good advice!

Yes Tony, unforunately the web is full of people who claim to find products that they've spend 100s or even 1000s of pounds on "unusable" unless they modify them beyond all recognition.

I recently bought a Blackstar HT-Dual pedal, and shortly before I did I found various people ranting at how they couldn't believe that Blackstar thought they could get away with putting such a crap stock valve in it, because the Thingy-Corp Vintage SuperTube was infinitely superior, etc, etc.

The fact of the matter is that Blackstar (and many others) make their reputation/sales by the sound of their kit, so they're hardly likely to risk that just to save a few quid on an inferior valve. True, there'll be an element of building things to a budget, but if it doesn't sound "right" in the first place, then it's not going to sell...

Of course, only you can tell what sounds "right" to you, so if you're set on the VHT, take Gary's advice, play it to death, and when at some point in the future you need to replace the valve(s), decide then if you go for something similar to stock, or something a bit "higher-grade".

If an amp, pedal or guitar that you're buying really does need half its parts changed before it meets your requirements, then you're probably buying the wrong one.

Si

[ef37a]

Thank you Garry and Cap' for your very sane contributions! I have run 100s of specification tests on (Blackstar) amps and pedals, some factory fresh, some loan artist models that have been thrashed for months. Rarely were the gain figures out by more than a few dB. Most often the pre amp valves were Sovtek, some EH some TAD 7025,little to chose between them. If a pre amp valve gave a noticable change in gain when fitted then CHANGED in a few days/weeks I would suspect it strongly of being faulty!

WRT to the valves in the Duals.These were exactly the same Sovtek ECC83 that was fitted to the top of the range Artisans. The only difference being that the front end valve, especially for the A30 was selected for low noise and hum. Such selection is not needed for the pedals since the HT and heater supplies are well regulated.

So do as suggested, give the amp a good rattling with the stock valve and (here's a novel suggestion!) RECORD IT!Then, when you part with far too much dosh for an exotic 83 you will be able to send us all clips of the wonderfully improved sound....Not!

If you want a suggestion for a good all round reliable spare dtriode the TAD 7025 is it and 6v6's can be had for about £5.00 but I have forgotten the name of the company! But then 6v6s never go wrong!

Dave.

[Folderol]

Evnin' All

Just like to add my 2d.

Being single ended, your output valve will be almost certainly using what's known as automatic bias, consisting of a fixed resistor and capacitor. Changing this wouldn't be a realistic option anyway. This bias method has the happy feature of making it very tolerant of valve differences which helps where aging is concerned and also makes it safer to try variations of valve type (provided it is pin compatible of course).

However, because all the different types of valves will have different characteristics they will also self-bias at different points. At low outputs this won't make a lot of difference, but once you get towards overdrive (which is where any civilised guitarists wants to be) it's a different story, so while one valve will tend to distort evenly producing most odd harmonics, a different one may distort more towards the cut-off side which will give more even harmonics.

[Gary_W]

Love the statement 'any civilised guitarist' - made me chuckle.

The chap I occasionally play alongside (a superb keys player) is of the opinion that finding a civilised guitarist is as likely as finding Bigfoot in the wine aisle at Waitrose. Like the bulk of my kind, I don't read music which only throws petrol on the BBQ of suspicion between the art forms of strings and keys

[ef37a]

Morning all.

Will, there is a schematic for the amp on their site. Looks fairly workmanlike except that they appear to have eschewed an HT fuse but fitted one in the heater winding! The OP stage as you say, is cathode biased, 470R 2watt (I would like to see 5Wish) and 22mfd. The anode supply voltage works out by my shakey math at 382V which is way over the normal limit for a 6V6 but they are known to be tough lil' beggers. That gives a cathode current of 42mA and a total valve dissipation of ~16W. Jeeust inside max spec but that is what guitar amp designers do!

The manual gives the usual warnings about "tampering and substitutions" so departure from the V6 is inadvisable? In anycase the only swop that might make a difference is for an EL34 but that takes twice the heater current and the mains transformer probably gets hot enough already! The 6l6 has a similar 0.9A heater requirement but since it is really just a "growedup" 6V6 not much sonic mileage there? AFAIK 6V6s are much of a kind, well, peeps go misty eyed about NOS Silvs' but pricey! There was the all metal V6 but that was pretty awful sonically by all accounts?

Depending how it is put together, a good testbed for modding?

Dave.

[Folderol]

Yes, quite a nice simple circuit - like the triode/standby option. Fusing is rather strange, but then there is a normal fuse and a thermal trip in the supply. Hmm, I wonder if the thermal one sits on the mains Tx.

I was more thinking along the lines of swapping in a 6L6 or KT66. If I've got it right the 6L6 was the forerunner to the others - including the 6V6 - and has a 'defect' in its response that would eliminate it for HiFi but might make it more interesting for guitar work.

P.S.
Why do so many designers draw bridge rectifiers in such a crap way?

[ef37a]

I think Will that is a NTC surge limiter in the neutral mains input.

Quite why they deemed it neccessary for such a piddling power pull I do not know! B's started fitting them for the Series ones, probably a good thing for the 100W, certainly the brute 200 and probably not worth risking changing the pcb for the 45?

I think some things are required for certain countries regs'? The heater fuse I think was for the Canadian market at one time?

Yes, weird waste of time for bridge! A rotated "square" is pretty universally understood I think?

You are correct in saying the L6 is a "hi fi" valve the V6 started life more for vertical deflection amplifiers I seem to recall? They are tho' pretty indestructable. I serviced a lot of radios yonks ago with the "Red E" series valves in them. Most used the EL33 (Ha! Bet most of yous have not seen one of them! You have missed nothing, crap reliability) but those with the 6V6 never had an op stage failure(of the valve) to my knowledge.

Dave.

[Folderol]

I think Will that is a NTC surge limiter in the neutral mains input.

I serviced a lot of radios yonks ago with the "Red E" series valves in them.

Hmmm {cogitate} {cogitate} {cogitate} {ping!}
ECH35, EF39, EBC33, 6V6GT
Yay!

Cossor Radio - had a small heater transformer but direct half-wave rectified mains with a selenium jobbie that ran along the back of the chassis.
Used to be our kitchen radio when I was a wee laddie

[ef37a]

Selenium solid state technology?!

Nah I am talking early 60's, valve rects' and the firm I worked for as apprentice rented out these radios, called "Bradios", somehow after the guy that made them I guess? Big and proper they were. Steel chassis mounted onto a very heavy Bakerlite moulding and a one piece moulding formed the cover. 8" speaker. "Lovely tone" the customers said.

The smoothers were 2x4mfd waxed paper blocks and these use to punch thru' and so Radspad cans were fitted. Waxy paper coupling caps used to leak and the 6V6 go red till a fuse popped, never died tho'! The valve lineup was as you say but there was a luxury model with an aperiodic EF39 front end and a SW band.

I used to LOVE lining up I.Fs etc. Wonder if the Superheterodyne principle is taught anywhere these days? Twas bloody clever you know wasn't it?

Dave.

Dave.

[Spyder2]

I have a similar single power tube 5Wer, the Rat Electronic mod of the GA5/Epi Valve Jnr.
I swapped the tubes for some posh ones. The power tube, EL84, made no discernable difference to me. The preamp, ECC83, did. I tried a few and they were all different in their ways, how do you like your distortion?, some broke up earlier, but the "poshest" one did win for me being more clear and present and dangerous (?!). Talking about distortion is like dancing about interference. So it's a case of trying what suits you with the pre-amp valves IMHO.
I can't remember what the valve was in the end for me, picked from Hot Rocks I think. Will check at the weekend.