output tube changeout

[Andy]

Hey Bill,

The book lists the ranges on page 195. These are all approximates:

OUTPUT TUBE
340-360VDC on pin3
300VDC on pin 4 (grid)

PREAMP TUBE
140-160VDC on pins 1 and 6 (plates)

RECTIFIER
320-330VDC on pins 4 and 6 in from transformer

I havent measured at A, B, and C, but the above is what you are shooting for.

[Rohbiwan]

Thanks AJ,

I unloaded the amp, powered er’ up and started testing voltages according to the book and as you suggested. All the values were within the given ranges give or take a couple volts. After some head scratching I loaded it back up with my test speaker and fed it a signal and WHAMO – it came right up!

Now to put it on a proper speaker with a guitar source and see what kind of tone I have. I appreciate the help.

Bill

[joewilly]

Bill,
I read your story of whoas. I had a few problems when I first fired up my 2 Stroke amp.I had a problem with the 9 pin preamp socket. Two of the pins were shorting against each other. Had to bend one pin and trim
excess wire protruding thru the pin.
sounds like you have the problem solved. Enjoy the tunes.
Joewilly

[Rohbiwan]

Been playing with it – minus a real speaker (using an 8 ohm public address speaker – it sucks).

So far I found that the solder joints attaching to the 1M pot covers were cold – causing intermittent loss of volume / tone control. Fortunately I got my new soldering iron in today and could crank it up to 750. I remember reading about that possibility.

I think next time I may pre-wire the tube sockets according to color code. Some are pretty tight like you mention Joewiley.

Some more fine tuning, shortening and routing of some of the PT wires and It’s cabinet time.
[attachment=69]itsalive.jpg[/attachment]

[Andy]

My favorite words coming from a Two Stroke builder… “I think next time…”!

[joewilly]

I had similar problem with soldering to back of pots. I SCORED SURFACE WITH 220 GRIT SANDPAPER AND USED SOLDER PASTE FLUX AND IT WORKED OUT GREAT. HOPE THIS WILL HELP YOU OUT.

[Rohbiwan]

[attachment=70]Twostrokev1.JPG[/attachment]

I got about 10 hours into the amp now using the 12″ in my Fender Blues Jr. and it sounds great. Frankly it sounds much better than I expected. There is a little bit of noise at higher volumes, but since I have not even trimmed the PT wires back yet I consider that a feature.

I have noticed some harmonic differences from what I am used to with the Fender. More burn in time required.

Thanks for all the help – Ill be watching for potential cabinet drawings.

Bill

[Robin]

There should be significant “harmonic differences” from the BJr, especially if the Billm mods have not been done. One of the coolest things about the Two Stroke is how harmonically rich it is. I found myself using less and less effects when I got my first Two Stoke going.

One thing you might try: because it appears that you have plenty of lead length left on the OT, try moving it closer to the middle of the chassis (away from the input jack) and see if it helps clean up the signal.
There should not be any down-side to moving it closer to the PT, but moving it away from the input and preamp section might help.

BTW, the Billm mods really transform the BJr into a great little amp.
I’ve modded a number of them and they all sound so much than stock.
Many times people change out the speaker trying to get the BJr to sound less boxy, but it’s really the flawed bias circuit that’s the cause.

[Rohbiwan]

Thanks for that, I read Billm’s page til my eyes bled!

I never really considered modding my BJr, but why not?

For the two stroke I placed the OT where it is for aesthetic balance, I think that moving it away from the input jack makes good sense, thanks for that as well.

Bill

[Robin]

All the billm mods are well thought-out and tested. Bill has modded literally 1000s of BJr’s. The bias mod makes the BJr into a way better and more versatile amp, and as long as you are doing that, you might as well do some of the others too. The “Clean Boost” add-on board is really a usable addition, adding about 10-11 db volume and makes it a workable gigging amp if you have to keep up with a loud-ish drummer. I’ve modded 7-8 of them myself and I’ve never heard anything but compliments about them.

If anyone else is interested in doing a BJr, buy one cheap, (you can find them with broken reverb all over the place) and do the mods. I’ve repaired several with broken reverb (easy and quick fix) for free and even if you end up replacing the reverb tank, a new one from AES is around $20.00 and much more durable than the original.

Except for the transformer upgrades and the power tube (to 6L6s)swap, I think I’ve done all the mods on one BJr or another.

[Peter]

Hi there, can someone please post a copy of the impedance chart as the link above is not working. Thanks.

[Author]

Posts