Dynaco lore - Differences between factory wired and kit built ST-70 - photos ..

Valvebloke

Thanks for those pictures they will be very helpful

Those Dayton capicators are absolutely new. They are sold by Parts Express here in the USA, and I think are a fairly reecent cap (last 5 or 6 years). I have an older ST-70 with the original driver board, and it is brown.

I think a picture of the underside of the chassis showing the wiring, would go farther in determining the age and builder/ modifications of the amp. Surely there is someone on this forum who can help you with the buzz, or humming problems, but I'm sure they will need to see the pictures of the internal wiring of the amp. Bob helped me considerably with my build of the M-125 kits I bought from him.

These amps are "keepers" and I, like you, want things to be kept as stock as possible to preserve the original sound, although sometimes replacements are needed to keep the amp in spec.

Good find, and I'm sure there are folks on this forum who will gladly help you track down any problems with the amp, and make it glorious again...

I'm curious - did Dyna assemble the ready to go amps at their factories in Philadelphia and later New Jersey? The reason I ask is I stumbled across a thread about Dynaco amps at another site, and a poster claimed that Dyna subcontracted out assembly of amps, rather than build them up at their factory.

Valvebloke mentioned in an earlier post about the transformer buzzing which I know is a problem for others as well. In my case, on a stock ST70 it actually was causing a hum in one of the driver tubes. Drove me nuts trying to track down the problem until I realized it was being mechanically induced.

I made a very effective isolation system for the power transformer. I used rubber grommets that had a .31" groove diameter that were about 1/4" thick and had an inner hole of about 0.200" along with some steel 1/4" long #6 metal spacers that measure about .200" OD and some #6 metal flat washers.

I unbolted the transformer and carefully opened up the mounting holes to 3/8" and inserted the grommets. Then I inserted the spacers through the grommets. If I remember correctly I had to change the transformer screws for some longer ones. I put a flat washer on each of the 4 screws and mounted the transformer through the new grommet/spacer mounts and put 4 more flat washers on the bottom with nuts and star washers. You can now tighten up the hardware snug to the spacers but the grommet remains relatively uncompressed so the transformer floats on the rubber.

The parts mostly should be available from your local hardware store and spacers through any place that carries electronic hardware lines like Keystone. If you use brass or aluminum spacers the will likely have thicker walls and be closer to 1/4" OD. You could use a 3/8" (.375") groove diameter grommet with a 1/4" ID.

I recently bought a Dynakit upgrade transformer and it appears that the screws on that are long enough to reach through my new mounts without having to change them.

It seems that my memory isn't what it use to be.

In regard to the transformer isolation the screws are #8 not #6. The spacers I used are considered to be #6 but are big enough to just allow the #8 screws through. If you can't find a suitable spacer to make the mount with the other option would be to change out the screws to a #6. I pulled the stock transformer and mounted the Dynakit HD unit last night and it fit perfectly on the mounts.

One more note if doing a mount like this. Be careful opening up the original chassis holes for the grommets. The holes will come right to the corners of the square opening. Start with an under size bit and go up in steps until you get to 3/8" or better yet if you have a tapered reamer drill the hole slightly under size and ream it to the final size.

Dynakitparts offers a transformer isolation kit, while not quite as elaborate as Ebill's solution, is still effective in reducing or eliminating the mechanical vibration transfer through the chassis, with no re-drilling required. Here is a link http://www.dynakitparts.com/store/product.aspx?id=255

Best Regards,
Charlie

Good point!
As my chassis was already modified I just dropped the new transformer in my mounts. However Dynakit did supply an isolation kit with the transformer. If this kit does it for you then great!
From what I understand the replacement transformers are quieter than the originals anyway.
I did my mod probably 7-8 years ago. The amp I have wasn't exactly pristine and I suspect that I had one of the noisier transformers on it. It is more work but it does float the transformer, its screws and nuts all from direct contact with the chassis. (not to mention I got all the parts needed from where I work!) So if you have a severe problem and don't want to spring for a new transformer..... If that hadn't done it for me I was going to float the driver board next!
What ever it takes to keep a classic going!

A few years ago I had a single ended power amp that was producing some mechanical hum from the power transformer. The audible noise turned out to be coming from the wooden shelf under the amp. Before searching for sorbothane feet to decouple the amp from the shelf, I tried a simple experiment that worked very well. I placed four art-gum erasers under the chassis in place of the rubber feet. Problem solved for less than two bucks!

Best Regards,
Charlie

One source of hum on the Mk-III was the fact that the chassies was made of steel and thus magnetic. Any stray magnetic field from the tranny made the chassie vibrate.
This made me replace my Mk-III with AR that was dead quiet from hum.

The new chassies from tubes4hifo is stainless and insensitive to magnetic forces ( which has their
own potential grounding issues, but with well tightened screws you won't notice any problems).
So replacing the steel chassie might be an option when refurbishing and oldie.

Did factory assembled Dyna amps ever come with the name Dynaco on the cage tag (the earliest/script style logo dating from the 50s), or did they always say Dynakit on the cage (with only the small, factory assembled tag stating Dynaco that was attached to the chassis)? When did the "modern lettering" Dynaco logo first appear? Did that only come with cages that were painted black? Did the "modern lettering" font ever say Dynakit?

I am not aware of any Dynaco old, script logo with the wording, "dynaco."

Nor of any Dynaco logos with the new style lettering and "Dynakit."

Always glad to be shown examples that violate the above, however. I haven't seen EVERYTHING.

Thanks!

Just to add a a bit of lore to this: Dynaco did not have a factory of any nature until it moved to Jefferson Street in Philadelphia. Powelton Avenue was a combination office/dual garage, single story building. "Factory Assembled" units were done by Drexel students on piecework, hence the great variety of wiring colors, styles of wire, rivets/screws/machine screws and so forth displayed over the years.

"Kits" were packaged and boxed by sheltered workshops, with components and parts supplied by various jobbers to those locations. And, each part, component and piece - other than transformers and tubes - were supplied by the lowest bidder of the hour. David Hafler was consistent with his tubes and transformers, however. In fact, in the early days, he did change his sheet metal source at least once. I do not know if this explains the differences that way, it might.

Jefferson Street (Across the Schuylkill river, in an equally marginal neighborhood) is a two-story, high-bay 'factory style' building of about 35,000 square feet that still exists. It is here that Dynaco first transitioned gradually from "piecing out" to having actual assemblers on-site. Their kit boxing and shipping was still done by sheltered workshops right up until the Tyco takeover, when all operations moved to Blackwood, NJ. Note that when Hafler started his eponymous company in Pennsauken, he went right back to his roots - the 'factory' being a two-bay garage with a small service bay and a few offices attached. Again, assembly was done by local job-shops and kit boxing and shipping by outside sources as well. I am not sure if the sheltered workshop relationship still remained, in my conversations at my one visit to that location, the staff was not very forthcoming, unlike with Jefferson Street and Blackwood.

Note that Hafler also farmed out it service functions to local shops as well, the service bay in Pennsauken was mostly for quick diagnosis. Anything more involved went out to a shop a few miles away, also in Pennsauken. I used them on several occasions as some of the early Hafler stuff was pretty rough 'from the factory'.

In any case, the history of the company and of its roots is quite colorful.

Yes, this is a few years late - but here it is.

To my knowledge all fact builds had a serial # kit had no serial #.

audiofreak1954 wrote:To my knowledge all fact builds had a serial # kit had no serial #.

The later kits (from the late 70s, anyway) came with a serialized sticker that one could initial and date. I expect few of them got installed, but I still have one on my FM-5 from that time.

Not sure about other units only the st70's. But no # on kits.

I just picked up another PAS-2. Figured since I have two ST-70's (actually an ST-70 and a VTA-70) I should have a preamp for each.

The person I bought it from said that back in the day if workers had extra time they would assemble PAS2 preamps. This PAS2 looks like it has has all original boards and components. The wiring is extremely neat compared to most have seen. The RCA jacks have completely different wire colors than just the regular green and red wires. The solder joints are very clean and almost all look to have the same patina.

Maybe this is just a neatly done rewire? I did see two diodes added to he the selenium rectifier. The solder joints here look shinier than the others. Too bad the OG tubes are missing.

No rivets. No factory labels. Haven't been home yet to listen to it. Work travel.

Hello everyone:
This is my first foray into this forum and I see some very interesting things concerning the Dynaco equipment that has been posted. I built a Stereo70 amp and a PAS pre-amp back when I was in college (~mid 60's) and used it for many years and was always pleased with its performance. That is where my background on Dynaco came from so when I see Dynaco pieces today, I understand the value in this vintage tube equipment. I visit a lot of estate sales and have seen Dynaco pieces on occasion. If I can grab some, I do, but it is tough unless you in the first 10 people who get into the sale. They don't last long.

So here is my question. I bought a Stereo 70 amp and a PAS-3 pre-amp which I intend to sell. What is the best strategy to do that on eBay? I found a local vintage stereo equipment person who will go through both items and make any repairs necessary (which he will charge me for) so that I can sell them as repaired/refurbished which brings a better price and gives me the confidence to sell them in that condition. The other option would be to post them on eBay in "as-is" condition and let someone else do the refurbishment. They are both in very good cosmetic condition but have not been powered up. I took the cover off both and cleaned up the dust etc. The PAS appears good and all there with nothing obvious wrong with it. The Stereo70 however has a cracked and smoky inside rectifier tube ( I believe #GZ-34) so I know it needs help.

Thanks for reading this and let me know your thoughts.

Thom