learning about my modified Traynor Mark 3

[stormbringer]

Hi all,

I've had a modified Traynor Mark 3 for 15+ years and am now trying to understand what the circuit. A bit about the overall mods: 2 channels, one clean and one overdrive (three gain stages, supposed to have a Dumble-esque quality), reverb on both channels, no more tremolo; I'll let you guess who modded it if you'd like.

[note: i've built an amp from a kit, but this is my first attempt at understanding an amp without a schematic; i have very little experience, so i'll spell out what i know below so you can gauge where I am at]

I measured the resistor values and checked out the cap values in the preamp section, and I'm wondering what is going on in the OD channel. For V2a/V2b, the plate resistors are 220k and the cathode resistors are 1.5k. V2a has switchable cathode bypass caps (either 22uF, .47uF, or none). I don't know what is going on with the V2b bypass cap. I've included some photos to help visualize what I'm looking at. First is a closeup of V2 just to show that I'm dealing with pin 3, which I imagine must be the cathode (pin 2 goes to volume, and pin 1 has a 220k plate resistor). that photo shows a blue wire heading out of the picture on the far left. the photo labeled 'V2b pin 3.jpg' shows where this blue wire ends up. I've circled a blue cap attached to the wire, which I believe to be a metalized polyester cap. The third photo shows this to be .68 uF.

Currently, my main questions are:
- is this supposed to be the cathode bypass cap?
- should this particular cap be used as a bypass cap?
- should the bypass cap be polarized?
- is this cap polarized?

That's all for now. Any pointers would be greatly appreciated!

-- John

[Jazz P Bass]

Traynor Mark III Schematic

I do not know what you are asking.
The bypass V2 cathode bypass mod is to reduce the bass frequencies.
The 22uf cap will pass all frequencies.
The 0.47uf cap will pass less bass.
With no cap at all the cathode will be operating with negative feedback, which will be the "cleanest" version.
These caps (22 & 0.47) should be polarized with the negative stripe to chassis ground.
I don't know what the 0.68 cap is doing.

[stormbringer]

Thanks for the input and for answering one of my questions: as I suspected, the bypass cap has to be polarized with negative to ground.

I am assuming this .68 uF cap is not polarized, so either this isn't the spot for the V2b bypass cap (i might have traced the preamp circuit incorrectly and got lost in there) or someone used the wrong type of cap for the bypass. Can anyone help me figure that out from the photos provided?

To clarify -
What I am trying to do: trace the preamp section for both channels. I am modifying a schematic of a related amp based on the values I am reading.
Problem: I think the bypass cap for the second stage of the OD channel is the wrong type (not polarized). However, I might be in the wrong part of the amp.

Additional questions:
- What would happen if you used a metal film (or some other nonpolarized) cap as a bypass cap?
- should I try changing it with a proper bypass cap?

-- John

[stormbringer]

update: I received the following info from the person who performed the mods on this Traynor:
- the cap in question is the cathode bypass cap for one stage of the OD channel
- cathode bypass caps do not have to be polarized.

Once I trace my way through the preamps a bit more, I will start to tweak the OD channel. I might look on the ampgarage for the trainwreck express preamp circuit. This could become a Traynor Wreck

The gut shots look 'messy', but the clean channel is really amazing. It is dead quiet and has better tone (to my ears) than the Allen Accomplice I built last summer and other vintage Fender models I've heard lately. I'd like to sell the amp to help finance other builds, but I think I'll keep it around for a while longer...

A couple of more photos showing the chassis and custom combo cab...

[stormbringer]

Here's another issue with this Traynor: It has a 3-prong power cord, but the ground prong is missing. I think I'll have this cable replaced by the local amp repair shop for $30 or so. The ground wire is soldered directly onto the chassis with no lug, so I'll have this improved so that there is a better mechanical connection.

I'd like to see whether there is any AC on the chassis. Is it possible to connect to the chassis and to earth? What is the best way to do this?

[J M Fahey]

*IF* the chassis is grounded through the green or green/yellow wire, you have a 3 prong power plug and your outlet is properly grounded, your amp *is* properly grounded.
No need for "extra" connections.

[g1]

JM, it sounds like the ground pin has been cut/broken off at the 3 prong plug.
You could just replace the plug, or if you want you can replace the whole cord and "upgrade" the soldered ground to a screw type at the chassis as you mentioned.
To test for AC on the chassis, connect one end of you meter to the chassis, the other end to the 3rd prong round hole in your wall receptacle. Measure the AC voltage. This is assuming your wall outlets are correctly grounded.
I hate to sound rude, but you are going to be doing modifications and other work but for something so simple as an AC cord you are going to take it into a shop?

[stormbringer]

*IF* the chassis is grounded through the green or green/yellow wire, you have a 3 prong power plug and your outlet is properly grounded, your amp *is* properly grounded.
No need for "extra" connections.

The green wire from the power cord is soldered to the chassis (albeit without a good mechanical connection). So is the amp properly grounded *even though the ground prong on the power cord is missing*? If so, how?

[Jazz P Bass]

Without the "ground" lug being attached to the plug, No, the amp is not "safety" grounded.
The amplifier circuitry is still commonly grounded.
The "ground" pin on USA outlets is the same connection, at the mains panel, as the white wire.
The reasoning for using another path is that the equipment chassis is "grounded" no matter what happens inside the amp.
If, among other faults, your mains power transformer develops a bad leak Vac to the chassis, the third wire will pop the panel breaker.
There was a post awhile back where the tube rectifier was injecting Vac into the chassis.
Hooked up a 3 wire cord & all was not well.
Blown panel breaker.
Did not know it until the third leg was hooked up.

[stormbringer]

JM, it sounds like the ground pin has been cut/broken off at the 3 prong plug.
You could just replace the plug, or if you want you can replace the whole cord and "upgrade" the soldered ground to a screw type at the chassis as you mentioned.
To test for AC on the chassis, connect one end of you meter to the chassis, the other end to the 3rd prong round hole in your wall receptacle. Measure the AC voltage. This is assuming your wall outlets are correctly grounded.
I hate to sound rude, but you are going to be doing modifications and other work but for something so simple as an AC cord you are going to take it into a shop?

Don't worry about sounding rude
I was considering taking it to the shop simply because it would be faster and cheaper than having a power cord shipped to me from an some online stores. Mojotone charges $25 for ground shipments to my address! It looks like Tubedepot.com is much cheaper, and I do want to do the work myself.

[g1]

Talk to the repair guy at the downtown L&M, he probably has some from Yorkville and they're quite cheap. Download the Yorkville sound parts catalogue:
http://yorkville.com/downloads/other/PartsCat.pdf
Any of the parts should be available through L&M and they are very reasonalble price wise.

[stormbringer]

Talk to the repair guy at the downtown L&M, he probably has some from Yorkville and they're quite cheap. Download the Yorkville sound parts catalogue:
http://yorkville.com/downloads/other/PartsCat.pdf
Any of the parts should be available through L&M and they are very reasonalble price wise.

Thanks for the tip about L&M. I'll give them a call.

[J M Fahey]

So is the amp properly grounded *even though the ground prong on the power cord is missing*? If so, how?

This may sound as a charade but it's not:
I mentioned a 3 prong power plug, obviously in its original condition.
A 3 prong power plug with one prong mising is not a 3 prong power plug anymore.

[stormbringer]

This may sound as a charade but it's not:
I mentioned a 3 prong power plug, obviously in its original condition.
A 3 prong power plug with one prong mising is not a 3 prong power plug anymore.

I appreciate your input; it seems something was lost in translation. I mentioned a three-prong power cord with a missing ground prong; I thought that was clear.

Cheers,
John

[Enzo]

Yes, you were clear that you have a missing third prong. Juan was discussing the need or lack of need for extra wiring, WHEN A COMPLETE THREE WIRE CORD AND PLUG IS INSTALLED. We know you need to replace the plug or the cord. You were asking in post 5 whether it was possible to connect the chassis to ground. WHEN YOUR NEW FULLY FUNCTIONAL THREE WIRE CORD WITH THREE PRONG PLUG IS INSTALLED, then your amp chassis WILL be grounded to earth.