New pedals and tubes... what do I do now?

[Patrick from Davis]

That is all you need to do for the Volume pot replacement.  The Fender one has an odd "frame" around it that must be unsoldered as well.  Another couple of tricks are to make sure that the Reverb pot is an audio taper, the reverb circuit is basically a mini amp in your amp so a linear pot doesn't make much sense, and to make a master volume in a pedal box that goes in the effects loop if you want to crank the preamp for Dire Straights-esque tones without creating a blast radius around the amp.

Other good ideas to think about with that amp, reflow the solder joints on where the tube sockets connect to the board.  They tend to take a beating.  This next point is one of the most common sources of trouble in these amps.  There are two wire wound 5 watt ceramic power resistors in the amp, 470 ohms, that should be replaced with 330 ohm (or close to that) resistors.  They are essential to the switching system in the amp, and they tend to overheat the board.  By dropping the resistance a little the problem goes away.  If you look at the solder joints on those two resistors, it can be quite ugly.  But for a couple of bucks, you can fix it yourself.
Patrick

 

[hannaugh]

Cool, thanks.  Looks like I have a laundry list of improvements for this baby. 

 

[Cagey]

Now... what does a cap job accomplish?  

A "cap job" can be two different things.

One is where they replace the power supply filter caps to keep them fresh. Those capacitors are of the electrolytic type, which have a lifespan to them. They have an electrolyte fluid inside that can dry up over time. When that happens, they lose capacity, and your amp's DC power stops being smooth. At the extreme, you'll hear a 60 cycle hum in the speaker(s), and the caps may overheat and explode. Before that happens, sometimes people will replace them as a preventative maintenance move. The typical time that's done is after 10 years, but it's not unusual to see amps go much longer on the originals. Modern electrolytics have longer life expectancies due to better packaging, so if you replaced some old ones today, chances are you'd never have to do it again. Also, if the amp is less than about 15 years old or so, it probably already has better caps in it, since the old style parts simply aren't available.

The second kind of "cap job" involves changing the various filter/bypass/coupling caps in the tone stack, effects and amplification circuits. Some people think different types of capacitors (mylar vs. paper over oil vs. ceramic vs. polypropylene, etc) sound different. They're usually Apple users or former drummers <grin> Fact is, the amp will sound different, but it's not because of the types of caps used. It has to do with their value, which is variable. Many electronic components have tolerance ratings to them, and caps can be amongst the worst. A .022mf cap might actually be anywhere from .018mf to .034mf or worse. So, changing them all will change the tone, frequency response, and overall character somewhere between not at all and quite a bit. Can't predict it, and can't say if it'll be for the better or worse.

Neither job is easy on the wallet. The first one is easy to do, but uses expensive parts. The second one uses cheap parts, but involves a lot of labor. Generally speaking, if you don't have a problem, don't worry about it. In other words, if it ain't broke, don't fix it.

 

[hannaugh]

Electrolytes:  it's what amps crave.  :laughing7:

Okay, thank you for clearing that up. 

 

[Patrick from Davis]

There are two wire wound 5 watt ceramic power resistors in the amp, 470 ohms, that should be replaced with 330 ohm (or close to that) resistors.
Patrick

Oops.  In case it wasn't clear, the 330 ohm resistors must be wire wound 5 watt ceramic power resistors as well.  These are the big ceramic box style resistors, about 1 inch by 1/4 of an inch.
Patrick

 

[Damon]

Also, I have heard that replacing the volume pot with an audio taper will give me more room to adjust the volume before my neighbors start to hate me.  Is this true, and if so, how do I do that?  Just de-solder it and solder a new one in, or is there more to it?

I, too, have a early/mid '90s Blues Deluxe and have done some of the mods mentioned above - specifically the power resistors and the second type of cap job, although with the intent of changing a few values as well as the slope resistor to get a slightly different tone, not because I think Orange Drops sound different than the ones that came in it - but according to the schematic I have, the volume pot is audio taper from the factory (250Kn15A, the A being audio taper). I think it's just a loud amp - aka a tube amp. Now the reverb is a linear pot and probably would benefit from being changed. If I had thought of that 10 years ago when I did the other mods I probably would have changed it, but I don't use the reverb enough to warrant pulling the amp apart just to change that pot.

Now I think I may need to break out the scope and see if the vol pot is really log taper. If it's not, that probably would be worth pulling everything apart to change it.

 

[hannaugh]

Let me know if it is an audio taper if you find out for sure.  I really didn't know, but yeah, it's freaking loud.  At 2 all of the neighbors in the apartment complex know I'm practicing.  At 4, they're upset and possibly calling the cops. 

 

[Cagey]

One of my brothers had a Fender Twin a few years ago that was funny with the volume pot. You almost couldn't touch the thing without the volume getting to be so high it was tearing your head off. I mean, that thing was outrageously loud! Reminded me of my Ampeg VT22, which was almost painful to stand in front of. I wonder if maybe that was a linear pot? We never did take it apart to check.

 

[Damon]

Okay, just pulled the back panel off and checked out the vol pot taper as best I could without pulling the board out of the amp. From what I can tell, it is an audio taper, but it's a pretty poor one. Very linear at the lower end, not showing much of a log scale until the upper end. So in other words, at bedroom volumes it might as well be a linear pot. Basically, audio taper pots are made by stringing together short strips of linear resistive material to simulate a true logarithmic curve. It looks like this one stays linear for way too long before the first transition area. Honestly, I think I'd just get a decent attenuator (might need to put a longer cable on the speaker to do it) instead of replacing the pot. That'll serve you just as well if you buy another amp later that gets too loud too fast. Weber mini mass or something similar would be perfect. That being said, if you can do the pot swap yourself and don't have to pay labor, it's a lot cheaper to find a good quality pot and break out the soldering iron.

On a different note, I forgot until I was looking in the amp today that I did replace bias resistor with a smaller resistor and a trim pot in series. Haven't changed the tubes in that amp in about 7 years (it doesn't get played much), so I guess it slipped my mind. Seem to recall it working pretty well now that I think about it. Don't remember what values I used, but if I find my old notes from when I modded that amp I'll let you know.

 

[hannaugh]

Awesome, thanks again! 

 

[Patrick from Davis]

My Hotrod Deluxe was this way as well.  The simplest cheap-o way is to wire up a "Master Volume" in a pedal box and put it into the effects loop.  You can get an attenuator, I did because I didn't know of some of the tricks at the time, but this is a very cheap version of that.  Either way, it will help with the, "yowsers," loudness.
Patrick