Trainwreck express questions.....

[marcoloco961]

Please forgive me in advance for my lack of knowledge on the subject of tube amps. I am extremely new to this, but am attempting a build. I have a couple of questions I am hoping some of the good people here could help me with, so my build goes as smooth as possible. Here goes……………… please don’t laugh too hard.


I am attempting a express build and I am having a hard time finding the preferred Orange drop cap for the .0022uf, or .0020uf 600V – C8 cap. I found the .1 and .022uf OD caps just fine, but not the other.

I have a 630V mylar .0020uf that I found a a electronics store here in town but it looks very old. I also have a .0022uf 1200V cap salvaged from a used T.V. and a couple of .0020 600V caps ordered from Allyn. None of the 3 are Orange Drops though

Question #1 is: Are the OD caps crucial at this stage or would one of the others work fine. And if so, which of my 3 options would you all prefer?

Question #2 : Most of the color coded layouts I have seen here show the toneslut OT secondary taps as gray = 4, yellow = 8, and red = 16ohms. The data sheet from hyboer shows the red tap as 4, yellow as 8, and gray as 16 ohms. Which is correct?

Question #3 : I saw somewhere that the 9.1K resistors on the PS board should be 3 watt as opposed to 2 watt. I am using the 3 watt version, will this affect my expected DCvoltages at my B+ terminals?? ( I told you I was new to this).

Question #4 : It seems ampwares parts division is no longer there. I cannot find the (5) pot grounding lugs anywhere. Is the copper grounding lug soldered to the rear of the pots not enough? Could I fabricate some sort of grounding lug if needed? Could someone please explain?

Question #5 : I am going to try and upload a pic of the shielded cable I have found for the input jack to the pre-amp tube, and the 7Watt 1K resistors for the power tube sockets to see if they are proper for this build. Keep in mind that I am not trying for a authentic wreck with all the original brand name parts, only ones that will offer a good sound replication.

Thanks for any input you all might have to help my build go smooth. It is much appreciated.

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[C Moore]

Hello -
In general don't use any "old, used, salvaged, NOS", components (except tubes).

1. Orange Drop caps are not crucial, unless they are crucial to you. They're just caps, use what you like.

3. 3 watts is the proper resistor.

4. Ampwares??? Good Heavens, they were a bad source when they were still in business. There are lots of good parts suppliers. Mouser, Parts Express, Allied, Hoffman, Metro, Weber, Mojo,.... the list goes on and on.

Good Luck

[paulster]

I am attempting a express build and I am having a hard time finding the preferred Orange drop cap for the .0022uf, or .0020uf 600V – C8 cap. I found the .1 and .022uf OD caps just fine, but not the other.

Allied are your friends when it comes to the Cornell Dubilier PVC series of caps. http://www.alliedelec.com

Most of the color coded layouts I have seen here show the toneslut OT secondary taps as gray = 4, yellow = 8, and red = 16ohms. The data sheet from hyboer shows the red tap as 4, yellow as 8, and gray as 16 ohms. Which is correct?

It should be red 4, yellow 8 and grey 16. That's for the Heyboer/Toneslut and Pacific transformers.

[marcoloco961]

Much appreaciated guys. Does the shielded cable and 7w resistor pictured look acceptable for this project to you?

I am still confused on the groundind lugs for the pots. As I understand they are a basic grounding lug for the pots with a long tail which is bent back and soldered to the copper romex buss on the back of the pots, correct? IS THIS REALLY NEEDED?

One more question................I recieved all linear pots from the supplier. I read here somewhere that if you use a linear pot for the 1M volume it will cause distortion very bad at low volumes. Should I use audio pots for all 3 1M pots, or is it only crucial at the volume control?

Thanks people, this is a really educational project.

[paulster]

Much appreaciated guys. Does the shielded cable and 7w resistor pictured look acceptable for this project to you?

They'll work just fine. RG58 is nice and low capacitance.

I am still confused on the groundind lugs for the pots. As I understand they are a basic grounding lug for the pots with a long tail which is bent back and soldered to the copper romex buss on the back of the pots, correct? IS THIS REALLY NEEDED?

They're a nice idea, but not essential. You can solder to the back of your pots unless they're stainless steel.

I personally don't like soldering to the pots as they need to absorb a huge amount of heat before you'll be able to solder to them, so I create a buss bar of the appropriate length and anchor it to two additional eyelets on my boards.

It all comes down to personal preference at the end of the day.

One more question................I recieved all linear pots from the supplier. I read here somewhere that if you use a linear pot for the 1M volume it will cause distortion very bad at low volumes. Should I use audio pots for all 3 1M pots, or is it only crucial at the volume control?

A 1M linear pot will function exactly the same as a 1M log pot electrically, despite some ill-informed indications to the contrary that you'll find on the net.

It will, however, be difficult to get any sort of granularity at the lower end of the scale which, in the case of the gain pot, will mean that it'll go from clean to scream probably before you've got to 2 on the dial, and won't do a lot thereafter. The effect on your tone controls will be similar.

I'd change the pots because I think you'll find it being a real headache, especially with this amount of gain on tap, and swapping the pots once you've got them all wired in (especially with solid core) is going to be an even bigger headache.

[marcoloco961]

Good info Paul, thank you very much. Now is the time to make the changes, before I fire up the soldering gun.

[Structo]

Well Marco,
You certainly picked a great amp for your first project.

Although from what I gather they can be a bit of a temperamental build.

The one tool I have to recommend besides a high quality DVM is a decent soldering station.

One with a variable temperature range is best, that way you can dial in the best temperature for the task at hand.
If you are soldering something heavy duty like the back of a guitar pot, it can handle that.
Down to simple 24 gauge connections as well.

I like the Xytronic 379 I bought a lot and for $50 it was a bargain.

I bought it at Howard Electronics, they have a lot of different soldering stations to pick from.

http://www.howardelectronics.com/xytronic/379.html

[marcoloco961]

Structo, I have an older, but pretty decent DVM. The soldering station is on the top of my list of soon to buy items. I have been using heat sinks for the delicate components.

Paulster, I read an old post where a guy was having trouble with a hum. You shared a neat trick using headphones on the secondary of the OT for placing the PT and OT to eliminate hum from the magnetic field interaction. Just for shits and grins I tried it on my proposed layout. What a difference an inch makes in the placement of these components. It went from a considerable hum where I had intended to place it to almost completely quiet with about an inch of movement.

What other cool tricks you got up yer sleeve????


Also when using the headphone trick the volume through the headphones was loudest on the red tap (4 ohm)? and quietest on the gray (16 ohm) tap. Is that how it is supposed to be? I would have thought it to be the opposite. Or is the red my 16 ohm tap?