"P2P" -- as in "point to point" :)

[mhardy6647]

An interesting countermelody has emerged in the Carver Crimson 275 review thread related to layout, wiring, and construction of vacuum tube audio equipment.
I thought it might be both interesting & fun to run a little bit with the topic of vintage wiring schemes, particularly point to point.

The Carver thread, e.g., shows a pretty typical consumer point to point wired product from (if I had to guess) the early 1960s.

Carver Crimson 275 Review (Tube Amp)

So you basically bypassed the grounding resistor used in the amplifier? This is how Carver says to measure the amp I order to not bypass that resistor. Load to speaker terminals, FFT ground to audio ground. This was addressed in the previous review I posted already. The sweeps I posted...

www.audiosciencereview.com

Pretty ugly, as the old oxymoron goes.

Another pretty ugly example of my own ken: the low-end (but popular) Pioneer SX-34/SX-34B, also sold by Allied Radio Electronics as the Knight 333. This was a late-era, all-tube AM or AM-FM stereo receiver, available until the late 1960s as a bargain priced hifi receiver. It used 6BM8 tubes (a combination triode and power pentode in one bottle) in a push-pull output configuration for about 8 wpc. It was small and very attractive... until one looked under the decks.

It is so cramped and crowded that sourcing replacement coupling capacitors that would physically fit was a bit of a challenge!

As other posts in the 'review' thread have mentioned, there were much better implemented point to point efforts.
The Marantz 8B is a good example.

This is the 'before' photo of one I had the privilege to rehab some years back. Very nicely and purposefully laid out and constructed, I'd opine. A pleasure to work on and a delight to listen to -- still one of my very favorite commercially-produced vacuum tube amplifiers.

Avery Fisher's company ("The Fisher") had his group of German engineers ("The Dutchmen") who designed the classic Fisher components. To my mind, they did a nice, thoughtful, and decidedly Teutonic job of layout in the 1960s-era Fisher stereo receivers. Not coincidentally, I enjoy rehabbing these -- they're easy to work on and sound very nice once freshened up a bit, too.

Here's a "before" photo of a Fisher 400 receiver from the mid-'60s illustrating the clean, open, and logical layout of this entry-level (and very successful) Fisher product.

Finally, there were also manufacturers, such as McIntosh, who used turret board construction to good effect.
I haven't "done" any Mac amps so here's a borrowed photo of the innards of my own favorite Mac vacuum tube component: the venerable MC-225 stereo power amp. Not so functionally "logical" in terms of tracing out a circuit, but neat, elegant, accessible, and easy to work on. Early Mac ss componentry wasn't all that different underneath.

I guess my point -- if I have one! -- is that point to point wiring quality and design ran the gamut.

FWIW, I still like point to point for vacuum tube amplifiers -- heat was not kind to early PC board vacuum tube hardware, although modern PC board construction materials & design may be more robust. I am also not a fan of PC board mounted tube sockets, due to the stress that putting tubes into sockets (especially tight ones) puts on the board(s).

 

[Deleted member 21114]

Smartphones must have been *huge* in the sixties.

 

[Cougar]

Don't see anyone commenting on these unit's grounding and how they are so dangerous.

 

[egellings]

Point to point makes sense when trying out prototypes, or if all you are doing is onesie-twosies. As an example, my tube mono-blocks & preamp are point to point, since I'll never make another set of them. For production quantities, the PCB makes the most sense. For analog audio, both types of assembly can work well. For RF stuff, where the strays are part of the schematic, like it or not, then the repeatability of the PCB, as well as ability to do transmission lines on them, is needed.

 

[Blumlein 88]

I wish I had it handy for a photo. Perhaps the worst I've ever seen was a Sansui tube receiver. I picked it up for $1, and it had some odd tubes, but for most I could rewire the pins and substitute. Was a beautiful unit with a thick stainless steel faceplate. When I looked underneath, I just gave up the idea. A rat's nest is neater, and boy did they use complex circuits for vacuum tube days. I think I still have it somewhere, and intended to use the output transformers in a fresh design of my own doing.

They must have been the precursors to late 60's and early 70's Japanese SS design philosophy. The best description of that I've heard was, "why use one transistor when 10 will do just as well."

 

[egellings]

I remember the pocket radio days, when transistor count was a supposed proxy for quality. 6 transistors were all that were needed to make a decent super-het pocket radio, with 8 being a deluxe job. Then I started seeing 16 transistor ones and was wondering what all those "crystal valves" could be doing. Two were used as diodes in the detector, and others had their 3 leads tied together and were simply soldered into holes in the PCB traces. It was a 6 transistor set, functionally.

 

[Blumlein 88]

I remember the pocket radio days, when transistor count was a supposed proxy for quality. 6 transistors were all that were needed to make a decent super-het pocket radio, with 8 being a deluxe job. Then I started seeing 16 transistor ones and was wondering what all those "crystal valves" could be doing. Two were used as diodes in the detector, and others had their 3 leads tied together and were simply soldered into holes in the PCB traces. It was a 6 transistor set, functionally.

I had one that touted 12 transistors right on the front of the radio.

 

[egellings]

My Kensigton pocket radio bragged 16 transistors right on the front bezel, too. I think transistor count was a selling point.

 

[Blumlein 88]

IC in this one.

Eight transistor Emerson.

Uses tiny transistors and not bulky tubes! True Super-Het.

 

[novice]

is that point to point wiring quality and design ran the gamut.

...and the gamut was all over the map!

LEAK is a good example of clean P2P, in the case a Stereo 50 (PP EL34). Convention nearly that of WW2 on comm gear, note the lacing -

But also note the amount of wiring heading under the board. They can be a bear to sort out and redo so they retain the original look. If there is an issue under the turret board all connections on 1-2 sides have to be unsoldered to get at it. There's a Saturday afternoon gone!

The other approach is to use turret sockets. What's nice about these is components related to that tube are local and all connecting wires easy to trace out. It's similar to the concept of distributed node modularity -

A real treat is to come across a piece of ham gear built by ex-Signal Corps military. Some are just amazing, even humbling; all solder connections perfect, wiring carefully measured, cut, & laced with no surprises. The only possible explanation for "rat's nest" chassis wiring is that the design goal was the shortest possible path between connections. When building on a flat plane (most tube amp chassis) that's what you'll end up with. But those can also be a bear to service as wiring may go over components needing attention so they need to be unsoldered too. My own personal pref though is much closer to the LEAK and less towards the jumble. With some forethought you can achieve great layout, ease of service and minimal wire lengths. Below work is not mine but 100% DIY. Would feel pretty good if I bought this and opened it up. Not perfect, would do some things differently, but it's all moving in the right direction (to my eye) -

 

[novice]

When I looked underneath, I just gave up the idea. A rat's nest is neater

I had a quad receiver that became intermittent. Reaction upon opening it...