Peavey Pacer Tube Amp Conversion Project, Part 1

Recently I bought an old funky Peavey Pacer from someone who had it on craigslist. Even though the seller was asking less than a couple Jacksons for it, and re-posted it every couple days, it was still unsold after a month. That's not surprising, since there were only two rather claustrophobic looking photos in the listing:

I replied to the ad after noticing something almost hidden at the bottom of the second pic - the speaker was a Carvin branded "British Series", made by Eminence and known to be an excellent guitar amp speaker. At the asking price for the entire amp, I figured it was worth it if the speaker alone was in good shape. On the phone, the seller said the price was negotiable since the Pacer had some "issues" - it would shut down after a couple minutes of playing, but might stay on long enough to check it out. Well, why not - it was only about three blocks away, so I grabbed a guitar and walked over.

Although solid state, Pacers have a solid rep for decent tone, as well as being really loud, and that's the way this one was. Right away it was obvious that the Eminence speaker was in good shape; I turned the Pacer up to ear bleeding levels (60+ watts!), and the Brit Series didn't flinch. As predicted, the amp's volume soon dropped to less than 1/4 what it had been, but okay, I'm sold. I handed over some cash and took it home.

The picture at the top of this blog post shows the Pacer as it was at that point, and here's a couple more:

 Here's the speaker:

Yup, that's an Eminence, and also yup, that's a boo-boo on the cone, repaired with a bit of black goo. Luckily, the hole in the cone, and the goo, don't affect the sound of the speaker at all. However, it took quite a while to clean the Brit up, in fact, the whole amp was pretty cruddy.

As a double check, the Pacer's amp was bypassed, and the Carvin British hooked directly up to a known good tube amp here, and it sounded very very good - efficient, balanced across the tonal spectrum of an electric guitar, able to handle a lot of power without becoming overly compressed, yet with just the right amount of breakup at higher volume or on dynamic peaks when you're really digging into the strings - nice.

And why is the speaker called a "British Series"? Good question; maybe Carvin was trying to capitalize on the tonal reputation that the older English made Celestions had. But this doesn't sound anything like a Celestion, but rather, just like what it is - one of the better models from Eminence, and in many ways superior for most styles of music than any Celestion. If I had to compare it to any other speaker I've ever played through, the Carvin Brit's tone and efficiency is very similar to that of a late '60s Jensen C12N.

I wasn't going to repair the Pacer; just happy to get a nice toneful speaker, which I was planning to put into a Leslie cabinet. However, the speaker output plug looked a bit suspicious:

I should have taken a photo of the inside of that plug - it was a mess, and the resistance between the plug tip and the the other end of the wire was over 120 ohms. Whoa - maybe that might have something to do with this Pacer's "issues", as the seller called it. I clipped the plug off, and soldered on a new old stock Switchcraft right angle plug:

Turned it on, plugged in a guitar, and torture tested the amp for over a half hour - no problemo. The repair, if you can call it that, only took ten minutes; so cool, now I have a usable amp for not very much bucks, even if it doesn't have any tubes.

My hypothesis is (could be wrong, I'm not a transistor amp repairman) that the incredibly high load on the pair of output devices, 1,500% of rated value, caused them to run so hot that the thermal sensor on the chassis, located between the two big TO-3 sized transistors, went into protect mode, and lowered the circuit voltages enough to save everything from going up in smoke. When the transistors cooled down after shutting the amp off, the sensor would allow the amplifier to run at full power again, until it overheated and go into fail safe mode once more. The Pacer's designers knew what they were doing, and that's great.

Here's a picture of the innards - note the thermal sensor sitting between the two output devices, which use the amp chassis as a heat sink:

As long as I had the amp torn apart, I cleaned it up as well as possible, got a new plug for the AC cable, and since one of the control knobs was missing, a set of old-school radio knobs were put on:

That amp was filthy, but now it's all cleaned up and ready to take to a jam, which I did. I thought the Pacer sounded okay enough for a $20 amp, but wow - I sure wasn't prepared for all the rave reviews it got. Here's a couple examples: "Your new amp sounds horrible!" "That's the loudest piece of sh*t I ever heard!", and my favorite: "I never thought I'd say this, but suddenly your tone really sucks!"

Well okay, the people have spoken. But the Pacer isn't really a crappy amp, it's just me not knowing how to use it. I've played exclusively through tube amplifiers for so long, maybe I've become overly dependent on the natural compression and singing sustain that comes with glowing hot vacuum bottles in a cranked tube amp. But whatever, they were right: suddenly, my tone really did suck.

As a reality check, over the next week I played through the Pacer at home for hours, and it sounded not great but good enough. The problem was that in a band situation, I didn't sound good playing through it. At the next jam, I used a Fender Blues Junior, and all was good again. Oh well, I ended up with a great sounding speaker, and that's why I bought the amp in the first place.

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A friend, David in Mass, hipped me onto the fact that some of the Peavey amps of this vintage had finger or dovetail jointed solid pine cabinets, and suggested I take a look at the Pacer's cab. Sure enough, it's a quality made, lightweight pine cab, although the baffle is a heavy piece of low-grade particle junk board. As a bonus, the amp chassis seems very suitable for a tube amp conversion build, so my course was clear: I decided to turn the Pacer into a home brew tube amplifier.

After a tear down, all of the Pacer's components besides the baffle, cabinet, and chassis, were sold on eBay for what the buyer, a Peavey aficionado and experienced repair guy, considered a fair and low price for a working circuit board and misc useful parts:

Minus listing and sales fees, and PayPal's transaction charge, I was able to net a bit more than what I'd paid for the amp, and the aluminum trimmed baffle board was given to a neighbor who thought it would look cool as a decoration in his music room:

At this point, I've ended up with a fine sounding speaker, as well as a usable amp chassis and a well made combo cab (minus baffle), for a total cash outlay of less than zero. My kind of no buck/low buck project, for sure.

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In Part 2 of the Peavey Pacer Tube Amp Conversion Project, we'll make a new baffle from a piece of 60+ year old solid core plywood, and start laying out the chassis for a tube amp conversion. In the meantime, here's a photo in process: