Original Trainwreck Resistors

[Littlewyan]

I've searched and searched but can't find the answer. What resistors did the original trainwrecks use? They look like 1/2W but what brand were they?

[RockinRocket]

Stackpole I do believe. If you go new production Stackpole let me know if they look like the ones Ken used.

[Littlewyan]

Just looked at the datasheet. The 1/2W definitely won't look like the ones Ken used. They're much smaller. Also according to the spec they have more contact noise than the Xicon Carbon Film.

The original resistors look quite strange to me as they're quite short and wide compared to today's production.

[Ron Worley]

Resistor form factors have indeed changed in the past few decades.

[Mark]

I hear people particularly on the Dumble forum say they hear a difference between resistors, but I can't say I have heard a difference. I built my Rocket twice due to complications I encountered, I used the standard Xiron resistors the first time and the later build with Takman carbon film resistors. I can't really say the amp was drastically different tonally.

I'm even careful to check the value of caps before listening for a difference. If someone knows a way to compare the different timbre of resistor types, I'm all ears.

[rp]

Anyone have some original Stackpoles on hand and can report if they are magnetic?

[Littlewyan]

I just ordered 1W Xicons to put into my Express. The 1/2W in there at the moment look a bit silly due to their size and I'm very curious to see if the higher wattage lowers the hiss. Also as the 1/2W are only rated for 350V I thought the resistors on the PI Anodes and the input to the Bias Circuit were a bit close to the limit for my liking.

I also ordered a single 100K RN65D to try out on a rainy day as I know a lot of people speak very highly of them.

[pdf64]

Anyone have some original Stackpoles on hand and can report if they are magnetic?

I don't know sorry, but can report that every tube I've ever checked has been magnetic, ie seems to contain elements that are attracted to a magnet.
Along with numerous other parts in a regular guitar amp signal chain.

[rp]

but can report that every tube I've ever checked has been magnetic

That's a pretty good point. Gotta run that past the hifi guys

[DaveWell]

Allen Bradley Carbon film 1/2W and 1W Maybe... i keep searching cause cannot find the 'Brand' Ken use...

To me,
If you don't want Magnetic issue go with the
Vishay / DALE CMF60 Metal film resistor
1/2W rated at 500V

Precision,stable and quiet circuit.

[Littlewyan]

I replaced all of the 1/2W Carbon Films in my amp with 1W Carbon Films and it made no difference whatsoever to the hiss. It measured at 70dB with the volume control on 10 and all tone controls at 5 before and after I swapped the resistors.

[DaveWell]

i had this kind of problem in one of my other built and the resistor as nothing to do with that hiss.

What I suggest to try is to:

Add a 820Ohm resistor on pin 7 of V1 and put a shielded wire to the volume pot. Ground the wire to the first pin of pot.

You can also add a 68K between the pin 3 and the input.

This will also help to keep RF away.

[Littlewyan]

Tried all that. The 820Ohm grid stopper added noise! Its not a problem, I was just experimenting to see if I can reduce the hiss.

[DaveWell]

Is can be from you 12AX7 tube

[David Root]

The new production Stackpole look a bit like the ones in Francesca, but the 1/2W new production are much smaller.

I bought some 2W ones because they are a bit larger than a typical 40 year old 1/2W, and at least look credible. Not expensive but not non-magnetic . Some have steel leads as well as end caps, some have copper leads. All have steel end caps.

I used some in my recently completed 4xEL91/M8082 8W amp, no problems. There's a gutshot in that thread that shows these resistors. Clean sounds very good. Had more trouble with microphonic preamp and PI tubes.