The Steel Guitar Forum

Do the Mid 70's session 400s need mod kits?

I mod'd my 74, but it needed new caps anyway, so I upgraded it. If yours works fine, probably no need. However, the old ones probably need recapped if they still have the original parts.

The question of 50-year-old electrolytic capacitors is not IF they will FAIL (they will) but when?
Sarno's mods replace the electolytics with polypros, which is a good idea.

Steven Paris wrote:The question of 50-year-old electrolytic capacitors is not IF they will FAIL (they will) but when?
Sarno's mods replace the electolytics with polypros, which is a good idea.

I didn't know Brad made mod kits. Nothing I could find on his website. Ken Fox is one who made mod kits for Peaveys.

https://foxvintageamps.com/classic_green_011.htm

I don't think Brad made a mod kit. He just listed the parts needed and photos of the 400 circuit boards to replace parts. I used his recommendations and purchased parts from Mouser.

I think the Peavey tone mods started with the Nashville series, the second generation, due to the change in the tone circuit and the speaker.

John LeMay was the first I knew of to do this back in the 90s. The Session 400 Limited, which was nothing like the original Session/LTD 400, benefitted from the mods, LeMay, Fox, Peavey as did The 2nd gen. Nashville, Vegas and other 400s from the same era.

I defer to Ken Fox et al Peavey tech experts, but other than caps and other component wear and tear from age, I wouldn't think you would benefit much from any tone mods on the original Session 400. The best thing you can do is be sure you have the proper speaker as a lot of them have been changed out.

The original speaker on a Session 400 with the chrome knobs was most likely a 1502-4 Black Widow with a ribbed cone and an aluminum dust cover. Possibly the first edition Black Widow Spider Web 1501-4 on the later black knob versions.

The very earliest ones were loaded with made for Peavey JBL K130s, but probably upgraded to Black Widows by 1977.

I have no experience with the several brands of recent neodymium speakers, but my choice, for that amp, would be the original 1502-4 SB BW.

Brad Sarno had a Session 400 Geek Page with pictures and suggested replacements for various parts. I can't find it on the internet now. After a soldering tutorial I carefully did my two Session 400's. I know nothing about how an amp works, but being very careful I got excellent results. Here's another Forum discussion: https://bb.steelguitarforum.com/viewtop ... 399d577d5f

I don't think the 1502 bass speaker was incorporated until the Nashville 400 evolved (1980's)? My 1974 400 came with the gray color D series JBL (optional was the 2@12EV speakers). I fried 2 of the 15" JBL's quickly and Peavey replaced them free of charge (I still have lifetime warranty on parts). Then they gave me the new 1501 replacement and all was good.

Dennis Detweiler wrote:I don't think the 1502 bass speaker was incorporated until the Nashville 400 evolved (1980's)? My 1974 400 came with the gray color D series JBL (optional was the 2@12EV speakers). I fried 2 of the 15" JBL's quickly and Peavey replaced them free of charge (I still have lifetime warranty on parts). Then they gave me the new 1501 replacement and all was good.

My original silver knob Session 400 also had the JBL speaker.

Brad Sarno had a Session 400 Geek Page with pictures and suggested replacements for various parts. I can't find it on the internet now.

As I posted on that thread you linked, Brad's pages are on the Wayback Machine (internet archive) here - https://web.archive.org/web/20180214233 ... 0page.html

IMO, the original Session 400 needs no "mod kit". But periodically replacing things like electrolytic capacitors and testing for other out-of-spec components is a good idea. That archived page of Brad's should head you in the right direction.

Dennis Detweiler wrote:I don't think the 1502 bass speaker was incorporated until the Nashville 400 evolved (1980's)?

Yes, I believe you are right. My bad. It was the second gen. Nashville 400 when they changed the circuit and went to the new SS version of the 1501-4 speaker. That's when John LeMay began modding the NV400s.

Thinking the early Session amps had either a JBL or the Spider Web 1501-4.

Dave wrote:IMO, the original Session 400 needs no "mod kit".

I agree... I think the later Peavey mod kits centered around op-amp replacement, and the original Session 400 has none, all discrete. That's a big part of why it sounds like it sounds IMO.

Bill is correct. op-amps in the later model 400 Limited and Nashville. The early amps had transistors, which gave it a warmer and fatter tone. It also had several 25v caps in the preamp circuit board that modded to upgrades to 50v caps and better quality caps. I think metal film? There may have been a few in the power amp circuit board?

No mods needed for session 400 or LTD 400 have repaired many just recap all electrolytics I replace main 5000uf with 6800uf 80volt caps tightens bottom best steel amps peavey made IMHO

Is there anyone out there that would do a LTD cap job for me if I sent the Chassie ?

I had a couple of Session 400 amps back in the 70's and 80's. Wonderful amps. Mine both came with a JBL M31 which was similar to a D-130F. Mine never blew. Regarding the quality of the parts... I bought a new Session 400 in the early 80's for an eight week run of Best Little Whorehouse In Texas. It started out sounding GLORIOUS. By the end of 84 shows, it sounded NOT-SO-GLORIOUS. I always thought it was due to component shift. I've heard that Peavey used very inexpensive parts which could support the "drift theory". This was as scientific a test that I was able to experience. Nothing moved. Same steel. Same player. Same settings. Same music. Has anyone else noticed the Session 400 changing (for the better or for the worse) over time?

T. C. Furlong wrote:Has anyone else noticed the Session 400 changing (for the better or for the worse) over time?

I haven't seen it with a Session 400, and I've owned a couple, BUT... I also didn't have a 'fixed' environment over a long period of time where such a thing would be noticed. As you know, every gig is a different world as far as what you can hear. I think the Peavey amp parts are probably +/- 20% kind of spec, pretty common in that industry, so it wouldn't surprise me.

What I have seen before during my 15 years working in a music store with amp repair, is a customer bringing in an old and tired (but working) tube amp for a 'tune up'. The tech would go through and replace electrolytic caps, look for other components grossly out of spec (and in some cases replace a tube or two) and then the customer comes and picks it up. He takes it home and we get a call the next day "What did you do to my amp!?!" it doesn't sound good anymore.

I think it's the same reason you can play through two identical amps, and yet they don't sound the same. If you get enough component tolerances all stacked up and 'leaning' a certain way, it can make an audible difference. I was on a quest for a Vibrolux Reverb a few years ago and visited my pal Steve at Austin Vintage Guitars.. (shameless plug) He had 3 or 4 from the same era (early Silver Face), and I went down the row until I found 'the one'.. it was amazing how different they sounded.

I like my Session 400. It is a 1976 vintage. It still looks and sounds like new. I did replace the JBL.

Discrete transistors are where the magic is on the early Session models. I'm finding the same to be true of circuits that use single ended JFETs.