1973 Fender Twin Reverb with rare JBL speakers

I played a Twin through high school. They're big, heavy and torture to take around. I'll never forget loading mine up in the back of my dads station wagon one night and he drove me to band practice (a Go Go band called Currency back in 1985!) and we took a corner and heard a crash. I was worried about my precious tubes. In Actuality it took out a window and the amp was just fine.....


About this amp. It's a nice one. This was a custom order one loaded with original JBL speakers and has the original foot switch.....

I'd never choose these speakers myself but when I do hear them I understand why someone would. Clean, big and bright. I actually like them in a black/silver panel Fender amp.

The complaint on this one was muddy sound, noisy intermittent reverb. It had some bad caps, needed a good cleaning, fresh output tubes and a NOS 12AT7 reverb driver tube. Never use a new 12AT7 in this position. They don't last and there are plenty of cheap 12AT7 tubes about....Sylvania, RCA, Telefunken, GE, anything but JJ or Sovtek!

This amp was also literally 7 resistors and 1 capacitor away from the original black panel circuit. I converted it. That's a part of that muddy tone one heard with these early 70's amps. It's worth it. The amp plays with a more open sound. Also re-wire the bias circuit so you can actually bias the amp. Get rid of that 'balance' arrangement.

Silver panel schematic:

Look at the phase inverter. That's where the "silverness" happens. Change it up to:

You may also change the 2 resistors in the power supply, but I prefer to leave those alone. A hair warmer in my experience.

You don't see many of these about here in NYC. Most of us prefer Deluxe Reverbs or Princeton Reverbs for these tiny clubs. So the prices are largely dependent on region. Some places you can get one for a bargain. You can buy one of these hand made amps for the price or less than a new reissue! Leaves me to wonder what the point is in those reissue amps. They are nice, but not quite as nice as one of these. Something to consider......

Idea on value:

https://reverb.com/marketplace?query=fender%20twin%20reverb

One like this with JBL speakers can command a high price, the rest, great amp for the money!

JB

Update on this: Client wanted a fresh set of preamp tubes as well. I'm a "if it ain't broke don't fix it" kind of guy but complied. When you change an entire set of tubes sometimes problems can arise. In this case one did. The tremolo started going 'tick tick tick tick'. No biggie. Simply put a .1 600V capacitor across the neon bulb tremolo 'bug' from the 10 Meg resistor to ground. I have little idea why this works, I'm just glad Jeff Bober showed me this trick 25 years ago! Saved me a lot of time over the years. I watched another tech painfully decline this and his customers Twin just kept coming back to solve the problem. The situation got tense. I told him this but he saw no logic in it understandably but he wouldn't even try it. I wasn't the tech at this shop and knew by suggesting this I was merely causing tension so I backed off. The customer backed off too and went elsewhere.....

Amp sounds great. Those JBL speakers have a richness to them. That's why they work so well for me. Clean but good, complex clean.

1976 Fender Super Reverb, end of the good ones.

This came in last week, belongs to a recording studio. The complaint? Harsh distortion at any volume.

First note, just a low E revealed this to be true. I felt annoyed. Sounded like bad voice coils. I did not wish to box up another four speakers and send them to California, not after the last 4x10" amp ('67 Marshall Bluesbreaker combo) had four bad voice coils. Made that telltale "THWACK" sound. Ruh Roh.....

But after opening the amp up I could see one electrical problem. The screen grid resistors were fried. I believe they were 1 watt resistors. Never use less than 2 watt.

After installing them I checked the bias. Each of the Sovtek 5881 WXT tubes were drawing about 4 milliamps. So, I re-biased for 35ma and the amp came to life.

This amp was rebuilt by someone years ago, new caps etc. They also did the black panel Fender mod which is pretty extensive. Worth doing. These amps have nothing really special about them so why keep a rather mushy sounding amp 'original' when it can sound great, and this amp does sound great. It's one of the last of the 45 watt models. They went to 70 watts about a year later. I really don't like those! The 70 watt amps are heavier (these are plenty heavy!) have an ultra linear transformer which I'm not fond of, lacks the power supply choke and no tube rectifier. The result is a harder sounding amp. Okay for country music if you need to play really loud. But for me? I prefer the softer compression a 5U4 or 5AR4 rectifier tube offers. These earlier models just have nice color to the sound, more warmth and more compression when you hit a note at high volume. Amps from this era can be a bargain. Still hand wired, still very high quality and easily modded to be close to the coveted 60's black models.

One more problem was noise. The reverb recovery tube was bad and the 2nd channel preamp tube for volume and tone had a good hum. That part was easy. The first channel had a good amount of snap crackle pop going on. And to make matters worse after replacing the load resistors and cathode cap, it didn't go away, it just became intermittent. Ugh. Some 70's Fender amps I've found the wire to oxidize and go noisy. I really hoped it wasn't that. Not up to replacing wires but if you do find this, start with the anode wires going to pin 1 and 6 on the 12AX7.

Fortunately it wasn't this. I found when it was in full crackle mode if I turned the channel all the way down it was gone (duh!) but also found if I turned the channel all the way up is went away. It only crackled in the middle. So I threw in a brand new CTS 1meg volume pot. Let it play for 2 hours and no noise. It's rare I get a volume pot that does this but I remembered my man Steve at Angela Instruments telling me this back in 1990 or so. Worthy of a try and it worked.

This amp has the original master volume and distortion circuit accessible through a pull switch. If I did the mods I would pull that bullshit out of there! The master volume never really gets dirty enough to justify having it in there, the distortion is comically bad sounding and the extra wires running around add a bit of hum. But like I said, this amp sounds great so if it ain't broke.....

For some ideas on Super Reverb prices, click here:

https://reverb.com/marketplace?query=fender+super+reverb

The 1967-1969 ones are some of my favorites once converted. But even the 1967 black panel amps aren't awfully expensive! You can spend way more on a boutique amp. Heck, I even built one for a client that set him back $1800 initially. He had every ultra expensive component mapped out for the thing. Top of the line Weber speakers, big ass Mercury Magnetics output transformer, every cap and resistor mapped out from years of "research" on internet forums. The result was the only amp I ever built that I didn't like. It was anemic. Another $1000 later it was exactly as I would have built it. Run of the mill Sozo caps, carbon comp resistors, cheap Weber Chicago series speakers, and the amp sounded like an old Super. Really great! And I was was baffled as to why anyone would go to the expense when an original is just not as expensive! Though, I sure appreciated the business, and he was a great client. Learned a lot about cap differences through his OCD tendencies. Literally, he would have me change one cap due to some jive he read on the web, but that one cap did make a difference....

I remember the first Super Reverb I ever heard. It was a Berklee Professor named Jim Kelly who had one and I saw him on a gig. I was floored by his tone. The second was my man David Lyons who now owns Sonic Circus (http://soniccircus.com/) in Vermont. After playing his my "new amp" phase abruptly ended. He had such a lovely sound. I no longer really play gigs big enough to justify using one of these but if I did, these are excellent workhorses. Tough as nails and really cut nicely.

Let's see. One these plus that Bluesbreaker equals 8 ten inch speakers....... Yeah, that's the ticket....

JB

1967 Fender Bassman amp

  Here's an amp I used to see all the time and haven't seen much of in a while. A good old '67 Bassman head built by Fender in Santa Ana California. These are to me some of the most consistently good sounding amps built by Fender, and are still relatively a bargain when compared to the earlier black panel amps. These are commonly known as the 'drip edge' series due to the aluminum edge around the grill cloth.

  This one is an AB-165 circuit. They started building this right around 1965. Not as desirable as the earlier AA-864 which, I ain't gonna lie here, is a better sounding amp. But these aren't bad by any stretch of the imagination. The AA-864 is relatively hard to find. I would describe it as more open sounding, the classic 'black panel' sound. These do have a bit more of a stuffy sound to them. You can convert one of these, it's a pretty big task so I wouldn't attempt it unless you have some serious skills. I've done several over the years with satisfying results. There is one thing I don't see talked about in literature and that is the output transformer may be wired out of phase on the AA-165. Once you do a conversion when you fire it up if it sounds like Armageddon (bombs falling, explosions, people screaming!!!) simply switch the blue and brown anode wires on pin 3 of your 6L6 tubes. Seriously, it's a scary sound!

  This amp just needed service. It had been off for about 25 years in storage. 5 out of the 6 tubes were original to the amp and unfortunately the 6L6 RCA tubes were shot. Always sad to see those go. I replaced them with Sovtek 5881 tubes, the thin base ones. They are rugged and sound decent. I like them the best cause I never get returns. All other glass is risky. The 12AT7 phase inverter tube I replaced with a NOS Sylvania. There are plenty of NOS 12AT7 tubes around, and in a Fender amp these, especially in the reverb driver circuit, take a lot of abuse. I get annoyed when I see new glass in these positions. The JJs and Sovteks fail. Don't be cheap and don't be lazy and besides, these often COST LESS than new glass. If you don't need premium Telefunken or Mullard, any garden variety RCA, Sylvania or G.E. will do.

  This amp received a full re-cap. Get those old, crusty electrolytics out of there! Yeah, they look cool and have those date stamps but, they need to go.

  Also check the power supply resistors. These were okay so I left them. Always replace the screen grid resistors though.

  I didn't convert this amp but did convert the bias supply. This is the era where Fender started to be more concerned with balancing the output tubes than actually biasing the amp properly. One tube stays constant, the other is adjustable. Not a terrible idea, Marantz has an individual bias pot for each tube, I like that. To do this really right you would need to add another pot to adjust overall bias, but we're just going to make it like the older amps.

  Now, on a late 70's model you need to leave that balance pot alone and add a bias trim pot. Here's why. Those amps are Ultra Linear. When one side drifts out the amp hums. I've seen people pay for a re-cap on one of those when all it was is the poor tubes aren't matched up right. I'm not a fan of ultra linear output transformers in guitar amps. The idea is low triode distortion at high pentode power. The result is an amp that is good for pedal steel or jazz but not as likable as the previous models.

 So Jef, what is Ultra Linear???

  Read this:   https://en.wikipedia.org/wiki/Ultra-linear

  https://www.ampbooks.com/mobile/amp-technology/ultralinear/


The Marshall Major, Park 150, Sunn amps, these are all Ultra Linear. I like these for bass. For guitar I like my distortion thank you!

  Anyway back to our Bassman. Once I got the amp re-capped and biased the amp ceased to hum and sounded great but still more needed to be done. Snap, crackle pop, hiss....... Here's an example of a big corporation trying to squeeze out every profit they can. Leo Fender was a perfectionist. He chose the best components available to him be it pickup wire or resistors, you know, the little things. CBS decided to buy resistors from Joe's Discount Resistor Shack, they probably just got a better deal on them. It's not unusual to have to replace EVERY load resistor in one of these along with the 220k and 470K resistors in that additional gain stage. Check them. In this amp all of them had drifted way out of tolerance. I replace them with new carbon composition resistors to retain that old, warm sound. There are plenty of choices. You can go with new Allen Bradley or Nichicon, Kemet, they are all good and I'm grateful I can buy these at Mouser, Antique Electronic or Mojo Musical. When I first got in the game I had to scour dirty, disgusting and often depressing HamFest or some poorly lit electronic supply houses. Ok, I did enjoy the HamFest and the surplus places, many of which are now gone were pretty special places. You met some really eccentric folks there. But that's ironic progress for you. A demand for a resistor that is by all means antique has created a new supply for us with picky ears! And that's exciting.

  It's the little things....

JB