HT 100 - Valve Replacement

[kanecharles92]

Hi Guys,

I know this question has been asked a million times over, and I've read quite a few posts on here for advice, but I'd like to ask again to reinforce my valve choices.

I have a HT-100 head (quite old now) and recently blew one of the TAD EL34 power tubes. I'm going to replace them, and figured it would be a good time to suss out some new preamp valves too.

At the moment, I'm thinking:

POWERAMP
4 * Matched SED Winged C EL34

PREAMP
2 * Tung Sol 12AX7 & 1 * JJ 12AU7
or
2 * Harma ECC83 Retro & 1 * Phillips jan6189w (ECC82)

I almost always play heavy stuff, usually living on the OD2 channel. From what I've read, the above valve combination should make for a very significant upgrade on the sound quality... I'm running it into a Blackstar 4x12 cab.

One other question, I've read that this head was to be biased at 100mV, can anyone confirm? I'd assume it'd need to change when putting in the Winged C poweramp valves...

Any input would be greatly appreciated, this is my first ever valve swap. I am fairly crafty with electronics and should have no issues performing the swap.

Cheers,
Kane.

[thephantum]

You can't go wrong with any of those tube choices.

The one thing I will say is that there is no "one size fits all" bias setting. Every tube is different and every amp is different. The only way to correctly bias a tube amp is to measure, calculate, set, rinse and repeat until dialed in.

[kanecharles92]

Thanks for that.

I was wondering, are these valves the Winged C ones that everyone is chasing?
http://www.ebay.com.au/itm/EL34-SVETLAN ... i80IM5k5SQ

I read that some of the rebadged Svetlana ones aren't the same as the SED ones that everyone raves about, even though these say they are NOS...

Also, if the amp is to be biased at 100mV, does that mean that the amp is to be biased at the same voltage even after putting the new poweramp valves in? ie I don't need to bias it to a different voltage to suit the new valves?

Thanks,
Kane.

[thephantum]

Yes, but technically they are not re-badged. Svetlana is location in Russia where the Winged C (=C=) factory is, but another company (New Sensor) sued for and now owns the brand name Svetlana. So there are =C='s that are labeled Svetlana (from prior to the lawsuit) and there are others labeled SED (from after the lawsuit).

The confusion comes in because New Sensor has Svetlana branded tubes that are packaged similar to =C='s. Bottom line, if it does not have the =C= logo on the tube itself, it is not a true =C=.



No. The amp should not be biased to a generic 100mV. Each push-pull pair of tubes needs to be biased and balanced based on the plate voltage as measured at each tube. You want each tube to operate at a specific plate dissipation rate, which it typically around 70%. Each tube is going to operate at a different plate voltage. Even matched sets have variances of +/- 5%. So each tube needs to be dialed in to operate at the same dissipation rate.

So, for example, by blindly setting 100mV, you have no idea if each tube is running "cold" or "hot". If it's too cold the amp won't sound as good as it is capable of. To hot and it'll sound pretty good, but most likely burn out much quicker. Because each tube is different, using a blanket, generic setting will most likely result in a mix...some tubes too cool, some tubes too hot. Will it work? Sure. But amps that are properly biased sound better, can get pushed harder and the tubes last longer.

Finally, for the record, B*'s come from the factory biased cold, so having it retubed and properly biased will most likely make it sound better than it ever has.

[kanecharles92]

Thanks for that thephantum, you are very, very good at explaining things.

As for the biasing, I have been advised by Blackstar directly that the HT-100 head does not have the capacity to individually bias tubes, as such it will need to be 100mV across the 4 matched tubes; should come close. This may sound like a stupid/noob question, but if Blackstar recommend that I bias to 100mV, will that be the same regardless of which EL34 brand I go? ie I wouldn't need to bias to a different value if I run a different brand? I haven't seen this answer anywhere written in black and white.

I think I am certain on selecting the Winged C EL34 tubes for the poweramp, I am just still not sure on what to use for the preamp... I've done a bit of reading on this forum (funnily enough, a lot of what I read was written by you ).

I have never tried didn't preamp tubes before, so this will be a bit of a guessing game. Luckily they should be a fair bit cheaper than the poweramp tubes.

Any tips/hints that you think could be useful?

Cheers,
Kane.

[thephantum]

Blackstar recommends 100 mA because it's extremely conservative. If you assume a plate voltage of 500V at each tube and then set bias to be 25 mA (25 x 4 tubes = 100mV), that's 50% of plate dissipation...a very "cool" (some would say cold) and thus conservative setting. Even if you assume a plate voltage of 600V (I doubt it's that high, but it's possible), you would only be at 60% plate dissipation.

They do this to allow for variations in plate voltages across different tubes. If the plate voltage is a little higher, the tubes run a little cooler. If plate is a little lower, the tubes run a little warmer. However, they never run so warm as to cause any problems.

Again, this is a very conservative approach. However, if you tune the amp to work with the specific tubes you'll be amazed at how much better it sounds. A very good analogy is setting a carburetor up on a hot rod: If idle is too low (cold) and it can stumble (or outright stall) when you hit the gas. Too high (hot) and the engine races all the time. If you get it set right though, the engine purrs like a kitten and is very responsive when you hit the gas.

As far as preamp tubes, keep in mind that you do not have to bias anything when you swap them....they are literally plug and play. So you do have the ability to experiment. In my own listening tests with new tubes, I have found that TungSols and Mullards are two of the best. I prefer the the TungSol as it's a little brighter sounding, but that's a personal preference. Both of those go for under $20 USD each. Hands down the best of the best is the Genaleex Gold Lion B759. When clean or with a lot of gain, it sounds very similar to the Tungsol. However, when you push it hard and it just starts to break up and overdrive, it sings with harmonics like no other modern preamp tube I have heard. I've only heard better from NOS tubes. That comes at a cost though, one tube will run you ~$45 USD.

My own recommendation is to put either TungSol's or Mullards everywhere in the preamp. If your wallet can afford a Gold Lion, put it in V1 (Clean). The other thing I would suggest is that the ECC82 be tested and verified for proper balance. That's the PI tube, so the more balanced the triodes are, the more even the signal is going to the output stage and the better the amp will sound. It typically costs 2 or 3 bucks more, so it's worth it...but only for the ECC82.