New Express project(s)

[joesatch]

this thread reminds me i have a transformer set for the express stored away. Can you link the chassis and bottom plate you used? Is it the BUD AC-412 and BPA-1520?

[dblgun]

Hey, the Bud chassis is a AC-425 and the bottom plates are the BPA-1520. As far as I know the bottom plates are still available from different vendors. The chassis are tough to get though. I was lucky to buy several back when you could still find them.

The AC-412 looks to be the correct length and width of 17"x 8" but the height is 3" rather than the 2"of the AC-425.

[dblgun]

Recently finished this amp and it turned out very nice I think. It took a bit to sort out as it had an intermittent problem with the presence potentiometer. I eventually found that the carbon track had a very fine crack that was causing the issue to get worse when the amp warmed up. I had a difficult time finding a replacement potentiometer and eventually found a similar pot that I robbed to repair the faulty part. It is very very loud which is what I remember about these amps, glorious! I tried it with some good attenuators and although they are good in my opinion the amps loses something that I am not willing to give up. Earplugs it is!

I have plans to get started on a lower output project using some vintage transformers and a pair of 6BM8's, so a bit more Liverpool. I will try to stay very true to KF's vision but expect the need for some slight changes in values to accommodate the different output tubes.

[joesatch]

What about this chassis? Anyone have experience with it? It appears to be .05" thick which is correct?

https://www.tubesandmore.com/products/c ... 16-x-8-x-2
and cover plate
https://www.tubesandmore.com/products/c ... 8-20-gauge

[dblgun]

That is similar but is 1” narrower than the original. The original layout in these amps has many of the components in very close proximity. There are some alternative layouts that may be conducive to the smaller chassis.

[Roe]

tubetown and ceriatone both sell chassises. the former is undrilled: https://www.tube-town.net/ttstore/tt-ch ... style.html

[dblgun]

Lots of options for chassis including those already mentioned, Modulus and several universal chassis makers on Ebay and Reverb, If you are in the market for a pre-punched chassis it limits the options. I guess it really depends on how anal you are about originality. I'm really picky so feel pretty lucky to have found a batch of Bud chassis. I've heard some great sounding clones with a number of different chassis, I think as KF did, the chassis does enter into the final product but I have idea how much.

[jeffkt]

very nice work!

[maxkracht]

Nicely done!

[Mark]

Lots of options for chassis including those already mentioned, Modulus and several universal chassis makers on Ebay and Reverb, If you are in the market for a pre-punched chassis it limits the options. I guess it really depends on how anal you are about originality. I'm really picky so feel pretty lucky to have found a batch of Bud chassis. I've heard some great sounding clones with a number of different chassis, I think as KF did, the chassis does enter into the final product but I have idea how much.

I’m inclined to think KF used the chassis that fitted his size, availability and cost requirements. I’m thinking the sonic qualities of the chassis wasn’t considered.

Of course I could be wrong……

[dblgun]

You could be right, its unfortunate that Ken is not around to weigh in on the origination of many of the physical parts used. There are some still out there that may have some insight to Kens thinking. That being said there are some indications that his selection of the specific BUD chassis was deliberate. When I go into local electronic supply house there are various metal and composite project boxes and chassis available from Hammond, BUD and others. BUD currently offers 45 different chassis options in the series used by Ken. The head cabinets that were used for Trainwrecks fit the chassis that Ken used and therefore I am assuming Ken designed it around the chassis. As I think about it, Trainwreck is the only amp brand I'm aware of that never ended up having a purpose produced chassis.

Comparative to the chassis and layout of many other well known circuits Kens designs have significant amount of unused real-estate. Fender and Marshall's initial builds were in very rough hand shaped chassis which quickly evolved into larger commercially produced chassis which continued to evolve for many years. Dumble used Fender type chassis and Gjika uses a Marshall type chassis. I think Ken could have just as easily used the smaller BUD chassis which would have made the amp smaller overall. I think he chose not to because of some very specific reasons. Clearly many have built Kens circuits, or at least variations, using different layouts and dimensions with satisfactory results. As far as I know John Mark still uses the original dimensions and layout albeit in a chassis produced by another manufacture. Just my 2 cents..

[Mark]

I remember Dave Funk telling me Ken used solid core wire as that’s what was available at the electronics store he went to. Dave thought it was funny that people thought Ken used solid core wire as it has special sonic qualities.

Perhaps the chassis he used was the most common one available at the same shop?
Maybe he want his amp to have certain look and that chassis ticked most of the boxes?

Probably a bit of everything.

I have one of RJ’s thicker chassis, I don’t have to worry about the weight of the transformers buckling chassis or dowels or bits of tape. It seems more practical.

The Komet amps offer some insights too.

[dblgun]

That is very interesting, I have never been to electronics supply house where stranded wire wasn't the primary option. My experience is it is often hard to find many options for solid core at most outlets especially for anything 20-22ga rated above 300v. I would also wonder why Ken continued to use solid core wire as he moved through the Express, Liverpool, and Rockets that he built. Alexander Dumble must have had the same issues where he shopped for his wire.

I have had no issues with the aluminum chassis but do not gig much with my clones.

[Mark]

I’m repeating what Dave Funk told me. That’s it. Factually speaking you don’t know what was in the store Ken Fischer frequented. You have used 6PS caps in your amp instead of the original Mallory caps. There was a time the Mallory caps were easily available. I have seen them in Fender amps.

Solid core wire does sit where you leave it which is a nice feature, but multi core wire is the better option most of the time, as many strands can break before the wire breaks.

You also have to look at the time frame the amps were built. They were built around the 80’s, if they bought wire in bulk that is a lot of amps and would account for one wire type being used. Then there is the historic angle, Fender amps were originally built with solid core wire and HAD and Ken Fischer may have simply been following that convention. There are a lot of possibilities.

That being said there are some indications that his selection of the specific BUD chassis was deliberate.

How so?
I would like to know why you think this?

I’m am sceptical of things Ken Fischer said, I remember when the Komet amps came out and it said that Ken used red wire as it sounds better. Somehow I don’t see this being factual, there have been many discussions over the wire on this forum.

What resistors did you use on your amp?
They look like Takman REX carbon film resistors.

[dblgun]

Mark, I am not questioning what Dave Funk told you and I sure wasn't in the store when Ken bought his wire. I think Ken and HAD used solid core wire by choice and not because it was all that they could get. I have had good luck using quality solid core wire in many applications and agree quality stranded wire is appropriate in others. As I said I have found high quality solid core 20AWG wire with insulation above 300v to be limited in availability and expensive. I have used Mallory, Sprague/SBE and CDE in many amps. I still have a small stash of Mallorys but like Mullard Mustard caps have started to be selective where I use them. I find the Spragues, CDE's and others to sound and function well in various applications.

As it relates to the chassis, like the solid core wire, I think as you mentioned it may have been what Ken found locally available initially. I think his design(s) were developed and refined in this chassis and he continued to use it throughout the years. I think he had a chassis, cabinet and the circuits and stayed with and refined these and other items as they worked. The components in his amps seem to stay very consistent and changes seemed to only occur when these items became discontinued, hard to obtain, overpriced or were inferior to something newly discovered. I think Ken wanted to use what he believed to be high quality components, potentiometers being one obvious example. With the majority of the parts occupying a relatively small portion of the chassis he could of moved to a smaller chassis but made a decision to not do so and only he could elaborate on this decision.

I have read and listened to a number of interviews and writings with/by Ken, he was very sharp. I think Ken was very meticulous in much of what he did and it was often taken, especially after his death, as a sort of a quirkiness. I think he would of been interesting to meet and that we would have gotten along well. I think that much of what often gets attributed to Ken ,or in some cases doesn't, is the effect of time. This can skew things sometimes to the extreme and repeated enough becomes things that some believe and pass on. I think that the facts are likely much more simple but less interesting. I think while Ken was still around he may have found humor in playing along with some of the nonsense.

I do like the Takman, Amtrans and TKD resistors in these amps and some others. I find that they are consistent, sound good and are rated higher with comparable body size to other resistors. The leads on the more recent standard 1/2 and 1w CF's have become lighter in gauge and shorter in length which I don't like. The downside is that certain values can be hard to find and they are much more expensive.