Question about trainwreck performance....

[redshark]

I'm bringing back this thread because probably by ending next week I will be firing up my clone, I will try to find a way to make a youtube video as soon as I tweak the sound. In this built which is my first express I will be using pacific trannies from Allyn. The only 2 things that are not high end is electrolytics (will be using F&Tand sprague) and pots (I will use CTS). Everything else is as detailed in the BOM.
I hope this 2 changes don't make a big impact on the tone. Well, really not expecting the pots to affect that much. But will carefully listen to the F&T caps. I know all caps need a breakin time anyway.
I have 2 matched pair of tubes that I would like to try, NOS tungsol 6V6's and NOS tungsol 5881, those last ones I know I need to make a bias change according to the trainwreck manual. Anyone has tried them before?

[paulster]

I have 2 matched pair of tubes that I would like to try, NOS tungsol 6V6's and NOS tungsol 5881, those last ones I know I need to make a bias change according to the trainwreck manual. Anyone has tried them before?

I've tried a few sets of NOS 6V6es in the Express and pulled them out fairly soon after and reverted to EL34s. They just don't hit it for me in that circuit.

I'd love to hear how you get on with the NOS Tung Sol 5881s though. Those are my absolute favourite tube, and even the new production are pretty good as well.

I may have to try one of my sets in the Express when I get a chance!

[redshark]

About biasing the amp I see alot of ideas here in the forum but I went and read the trainwreck pages and Ken wrote that the way to bias the express is to have -30vdc in pin5 and same applies using 6V6 or EL34. If you want to use other tubes like 5881, 6L6 etc you have to change probably the value of the resistor. Anyone can make comments about that?

[Structo]

I'll take a stab, measuring the bias voltage is not the best way to bias an amp.
It doesn't really take into account the plate voltage which is half of the equation.

Best to either use the shunt method or solder 1 ohm precision resistors on the cathode to ground.

Then use this formula.
---------------------------------------------------------
(W * .7) / V = I

Here W is multiplied by .7 to give us 70% of the tube's maximum plate dissipation.

This number is divided by the actual B+ voltage in the amp to determine what idle cathode current to adjust the tubes for in AMPS.

An example:
In an amp with 480V B+ and using EL34 output tubes (25W max plate dis.).

(25W * .7) / 480V = .036A

17.5 / 480 = 36mA

Cathode current at idle should be adjusted for 36 milliamps.

-------------------------------------------------------------------------

The guys here can tell you where they like to bias there amps in relation to the tubes used and voltage present.

[paulster]

Cathode current at idle should be adjusted for 36 milliamps.

That really ought to say, a maximum of 36 milliamps.

Wrecks tend to sound best when biased very hot though, so the suggestion of 70% will put you about exactly where Ken specified the ideal bias point.

Note also that the cathode current, if you measure it across a 1R resistor, will also include the screens current, as well as the plate current so the reading will be slightly higher than you expect.

You can either ignore this and give yourself a slight margin for error, or you can measure the plate current across the screens resistors and subtract this to get the true plate current.

[redshark]

Yes, I know that 70% method but the reason why I mentioned the -30vdc is according to the trainwreck pages written by Ken himself...

"the correct bias voltage for a TW express amp in operating position using a digital multimeter is -30 volts on Pin 5 of the output tube, which may be adjusted by using the variable adjuster inside the chassis. Normally, this adjustment will never have to be made. A special process at TW manufacturing headquaters insures that there will be little need for bias adjustment for many years!"

That should apply for both EL34 and 6V6GT according to the express manual.

If someone has used this -30 before aproximately how many mA's are the EL-34s drawing?

[redshark]

One more note from Ken...

"The TW express amp is unique in that is capable of using either two 6V6 or EL-34 output tubes. They can be switched without adjusting the amp. Because of this feature, a TW express amp should not be biased by current. Instead, it is recommended that biasing be done by the voltage method."

What I wrote in the last post details this method.

[paulster]

The voltage method will basically give you a bias figure of about 70%, so use whatever method suits you best.

With 5881s you'll have to use the current method though, as you've not got a baseline voltage to aim for.

[breakfastbuddy]

the voltage metode is just roughly . every tube are different even is label the same as el 34 . put in a 1ohm resistor and measure , but maybe roughly is good enough. within 10% is your goal i would say .

[Structo]

Sorry Paul that was a cut and paste manuver on the bias formula and was just given as an example.

Biasing with the negative bias voltage on pin 5 may be well and good if you have an original Trainwreck amp that Ken knew what the B+ was because he was familiar with what power transformer was in it.

But you take a clone that may or may not have the same PT specs and all bets are off.
As well as the differences in power tube sets being used.

Might just be me but I would never depend on a negative bias voltage value for biasing an amp.
You may have the same negative bias voltage as mentioned in the Trainwreck pages but maybe your plate voltage is different.
As you probably know, the plate voltage can vary depending where the bias current is set.

Power dissipation is I x E = P with the E being the plate voltage.

[dark]

It’s very interesting to read all these posts with good observations, especially from current or former original Trainwreck amplifier owners. Glen is my favorite, because he is very deeply in every aspect of: as owner of ORIGINAL amp, his playing style is indivisible from Trainwreck amps, and at last he made two very good clones. Apparently Kenny had something that many builders still miss and they are jealous that someone made something simple, very simple, something that they even can not replicate…

As former owner of original Trainwreck Express I carefully read posts here. If I compare pictures of Franceska with my amp I must admit, it has similar parts inside but placement of parts distinguishes sometimes 3-5 mm! My amp had NO Mallory filter caps! True is: no rules about Kenny’s amp! Making exact copy is probably safe way not to make big mistake but ART of Traiwreck amps is vision of the moment, THE ART OF POSSIBLE.

At last, a few times I tried to make dream guitars from “name” parts. It looked a lot easier but never happened…

Dark

Rock on!

[redshark]

Dark, very interesting comments from a former TW owner. One question, if your amp didn't have mallory caps then what caps were in yours?
This is my first build so I have not even 10% of the experience of the master builders here but I had talked to people that knew Ken and I had been reading lots of his ideosyncracies about amp building and I started to realize that the names of the amps probably came from the personality that each amp had, meaning all amps are built with components that have tolerances so every single amp will react in a diferent way even with same values and same circuit. Therefore some will be ballsier, some will be smoother, some will be darker, some brighter, all depends how all the elements interact together. Other thing that I had realize is that cloners copy mostly what they see but not what they hear and that is why the myth that only Ken could make them sound right.
I'm getting closer to testing the amp so guys wish me luck. I think by the weekend I will report here my results or probably questions of how to fix the mess!! who knows....
You never know how your potential "AMPSTRUMENT" will sound...

[redshark]

Job is done!!! the amp came back to life today!!!
Is very quiet, I was expecting noise as other people had reported here before but I think the attention to lead dress and placing of components paid me back big time!!!
Now is running on NOS 6V6's and is really loud. Very loud 22 watts.
I will try to get some Siemens EL34's next week and report my results.

Love this AMPSTRUMENT!!!

The cabinet I'm using is 2x12 old marshall with rola G12-65's but probably it could sound better with greenbacks.
Thanks a lot for your answers guys!!

[Glyph]

Does anybody make name plates for Trainwreck clones?

[Jana]

"Does anybody make name plates for Trainwreck clones?"

lol, that's going to get you a warm welcome for your first post!