Vintage Contruction Techniques - Tube Socket Mounting

[Fletcher Munson]

Looking at my old '59 Fender Champ, I see that the tube sockets were mounted with rubber washers or grommets. The socket is then connected to the chassis with a braided ground wire. I'm wondering if anyone knows, or can infer, the reason for this type of contruction. Is it intended to isolate the tubes from vibration, or is there something else going on?

[Tom Phillips]

Yes. The primary purpose is to isolate the tubes from vibration. The ground strap is then added to replace the ground path that was broken when the tube socket metal flange was mounted to the rubber grommet.

[Fletcher Munson]

OK, thanks. So I'll assume that Fender eventually abandoned this technique because they decided it just wasn't worth the time and trouble.

The grounding technique on this amp is... interesting. Ground wires soldered to the chassis scattered all over the place. Notice the wire from the OT secondary goes straight to the OT frame. Surprisingly, the amp is fairly quiet.

[Tom Phillips]

OK, thanks. So I'll assume that Fender eventually abandoned this technique because they decided it just wasn't worth the time and trouble.

Yes. The technique was actually very short lived. Fender probably just figured out that they could market adequate amps without the additional effort so the vibration isolation was sacrificed in the cost reduction process.

The grounding technique on this amp is... interesting. Ground wires soldered to the chassis scattered all over the place. Notice the wire from the OT secondary goes straight to the OT frame.

Yes. Classic Fender grounding.

Surprisingly, the amp is fairly quiet.

That always has surprised me too. The grounding was good enough for the low gain amps of the time. It is interesting how old amps sometimes get screwed up when someone tries to improve the grounding scheme by making incremental changes but do not work in concert with the old grounding left in the build. In those cases the individual changes are each better in theory. However, the individual changes may not work well with the old grounding circuits left in place. The point being that a grounding scheme must be designed as an organized system rather than a collection of individual parts.

[g1]

When the boogie-man started hot rodding Fenders the added gain gave microphonic/feedback issues so he re-introduced the rubber grommets at the first preamp tube (at least in the early boogies).
Some Ampegs use rubber standoffs to isolate the entire chassis from the cabinet.

[Rob's Radio-Active]

Yes. The technique was actually very short lived. Fender probably just figured out that they could market adequate amps without the additional effort so the vibration isolation[...]It is interesting how old amps sometimes get screwed up when someone tries to improve the grounding scheme by making incremental changes but do not work in concert with the old grounding left in the build. In those cases the individual changes are each better in theory. However, the individual changes may not work well with the old grounding circuits left in place. The point being that a grounding scheme must be designed as an organized system rather than a collection of individual parts.

Been there done that. I usually use a distributed star ground and shielded cables to the pots on my own design/builds because I could never go through as many trial and error grounding and routing schemes as Fender might have had to back in the day. The way some of them seem to have unshielded wires running willy-nilly everywhere and somehow don't hum or oscillate. I never get that lucky.
cheers
Rob

[Fletcher Munson]

Totally off-topic, but I have another qustion about construction techniques on this amp. Does anyone know what the greenish paint is that they used to seal/mark the nuts? I've seen this sort of thing on 50's electronics before and always assumed it was there as a kind of "loc-tite" and as a visual mark that the joint hadn't been tampered with. Anyone know how and why they did this? Is it just paint, or something else?

[Tom Phillips]

...Does anyone know what the greenish paint is that they used to seal/mark the nuts? I've seen this sort of thing on 50's electronics before and always assumed it was there as a kind of "loc-tite" and as a visual mark that the joint hadn't been tampered with. Anyone know how and why they did this?...

I think you nailed the reason. I don't know what the material is but since I've seen other old equipment using the same green stuff I think there is a good chance that a supplier marketed it as a thread locker. In the case of the shock mounted tube sockets it is needed because you can't use lock washers and torque down the nut with the rubber grommet under it. Today, we would use something like a nyloc nut in that application.

[Leo_Gnardo]

Anyone know how and why they did this? Is it just paint, or something else?

Generally paint of one sort or another. Some used an orange-red paint called Glyptol whose real function was hi voltage insulation, but there was a bottle in every workshop so it was easily available. In Japanese gear sometimes I see green or pink or purple tinted clear lacquer. Old Marshalls & other UK amps, blue seems to be the norm, dabbed on solder connections also as an "inspected" mark. Early on in my fixit career, the veteran techs told me fingernail polish worked just fine, pick a color you like or get some from the closeout-sale shop. On occasion I've seen cyanoacrylate (crazy) glue used, which sometimes gums up the threads to the point the bolt must be broken off or ground away to remove it, what a giant PIA. If this happens to you, might try a drop of acetone or nail polish remover to dissolve CA glue first.

[52 Bill]

Here's my take on the reason for dropping the rubber grommet mounting system. When these amps were originally designed, microphonic preamp tubes, especially the octals, were the norm. Adding the shock mounts could make the difference between and amp that was playable and one that constantly howled and whistled.

With the later use of the 7025, there was less need for the isolation so why spend the time and money for something that was no longer needed.

[J M Fahey]

In the 50`s the general purpose adhesive (except for wood) was nitrocellulose and nail enamel is just one version of it.
Anoher name was "speaker cement"
Now you know why those old Jensens are brittle and self disassemble.

Even today I buy a can of the modern version: nitro (if available) or acrylic "car paint base" , the transparent one which fills only 3/4 of the can on purpose, so you can squeeze pigment pouches in as desired.
That allows car painters flexibility in adjusting exact matching colours, even if car is off-colour (old/sun exposure/etc.)

As is, itīs quite liquid, so I let the can open for a couple days until it thickens into syrup or honey , to use as adhesive, including thread lock.

The beauty is that it stands vibration very well, but a little extra pressure with a tool snaps it open, very clean.

Other adhesives gum the threads, these do not.

In fact I save "honey"/daughter empty nail enamel bottles and fill them with nitro paint, to touch up scratches, screw heads, rust spots, etc. ,very handy.

[Fletcher Munson]

According to Wikipedia:

Thread-locking fluid was developed by American professor Vernon K. Krieble in 1953. His company, American Sealants, founded the Loctite brand. An early version of the compound was patented in 1960.

I didn't know Loctite had been around that long. The material on the amp could be a thinned paint, but it might just be Loctite.

https://en.wikipedia.org/wiki/Thread-locking_fluid

[mozz]

We used to call it q-dope, the red stuff was for high voltage but worked also. I bet most was just paint as why would they spend extra for a locking compound? I just ask the wife for a nail polish color she doesn't use.

[Tom Phillips]

...I bet most was just paint as why would they spend extra for a locking compound?...

"Hey Joe. Ya got any use for this leftover ugly green paint? Or should I just toss it?"

[Enzo]

I think they were doping solder joints before 1953, I certainly burnt through my share of the stuff desoldering parts from WW2 surplus gear when I was a kid. And of course hardware too.

In my shop I had a spiffy bottle of neon pink nail polish for doping nuts and screws. One cheap bottle from the dime store lasted ages.


DIme store was the 1950s equivalent of the dollar stores of today.