[morzh]

I have just finished adjusting my 80jr, and some time before I finished the 20, console version.
Both do not sound comparable to my Zenith 9s262.
I can hear distortion.

Both sound very similar (distortion-wise).

All the radios have been fully recapped (and I mean - fully), and re-resistorized.
All the tubes have been verified and are good-to-excellent.

80jr has A-class output whereas 20 has push-pull type.
20 has the speaker re-coned whereas 80jr has the original speaker which looks like new and does not have any damage (visible) whatsoever.

80jr has the original output xfmr.
20 has the replacement one (I think 125 C or D, a universal push-pull).


So, considering the quality is somewhat acceptable, but not stellar by any measure, is this something that maybe I should be expecting or is there room for improvement?

I can definitely put a sound signal in and watch the scope picture and see if it is distorted too much, but I have to get me a compact sound generator first.
But I'd like to understand if this is warranted or maybe I am trying to chase something that's mot there.

[murf]

I hear what your saying.
My Zenith consoles have much better sound and clarity than my philco's.
Puzzles me too.
Even my 38-116 15 tuber does not sound as good as my 10 tube Zeniths.
My 12 tube zenith has the best sound of all of my radios.
Let me know if you discover something.
murf

[codefox1]

Don't know exactly what you have, but the metal spiders of yore clamped down on a hole in the pole piece didn't help. Yet electromagnet speakers like the ones in Organs and high end sets can and do sound magnificent, and I have some. High end needs some help, if you can still hear it, but a waste of time for native standard AM reception nowadays which is pretty much (human) voice range compressed into commeercial noise.

If you're pumping better program content via local transmitter, sure you can do your best with alignment, output stage, speaker, and wow the old cabinets can really rock again. A really efficient speaker can get more out of a smaller amp. Look on web and compare. 150 watts into a public nuisnce car speaker may not be as good as 1 watt into a really nice old 8 inch full range speaker, but you decide.

[Ron Ramirez]

If your Philco 20 still has the original, solid, stiff spider, it never will sound very good. Add in the 24 power detector that is known to contribute distortion, and you have some serious low fidelity on your hands.

I have one of the early production 20 cathedrals that only has two trimmers. The speaker was reconed, using one of the open, more flexible spiders from an old 112 speaker. Result: much better, fuller, richer sound.

Now, the 80 was Philco's loss leader - the cheapest radio they made in 1932-33. Its $18.75 price was intended to draw people into the Philco dealer, where it was the job of the salesmen to try and talk the customer into a more expensive 71 or 91. The trick didn't work in late 1932, however, and nearly 200,000 80B Jr. sets were sold.

Anyway, as a dirt-cheap radio with a regenerative 2nd detector, its sound will never compare with a McMurdo Silver Masterpiece V. Actually, it will probably sound more like a 20 with the solid-spider speaker, even though the 80's speaker has an open, flexible spider.

My Zenith consoles have much better sound and clarity than my philco's.
Puzzles me too.
Even my 38-116 15 tuber does not sound as good as my 10 tube Zeniths.

Yep, those big black dials sure improve the sound quality. Something must be wrong with your 38-116, Murf. It should have an outstanding sound, especially with the treble-selectivity control turned up for maximum fidelity (treble) and the off-on-bass switch set to maximum bass. The 38-116 and 37-116 sets I've owned in the past sounded like FM radios on strong AM stations when set for maximum bass and maximum fidelity.

[TA Forbes]

If any of the mentioned radios in your (Murf's) post sound better than your 38-116, then something is definitely wrong with your 38-116.

[morzh]

Ron

Actually in my 20, as I said here, the speaker was reconed with the modern cone with no spider whatsoever. I did have the spider intact, the sole piece of the whole cone that surtvivded, but when they reconed it and sent it back, I noticed the spider was cracked.
The guys were pretty gracious about it, they took iot back and put a modern cone into it, so there is no spider to disimprove the sound.
But, I take it, I probably should rest with those and not worry too much.


Ps. I am talking about listening to exact same station on AM, which is local and plays gopod quality music. But the quality I only was able to appreciate when I fixed the Zenith.

O, well, I won't be modifying anything; the authenticity must be preserved.
However I will look at the sound output at some point; I am just interested whethere there are serious distortions in the output.

[Alan Douglas]

Ron has zeroed in on the detector stages. These were passable in the days of 30% modulated broadcast stations, but now, with higher modulation, and compression to keep it up there, distortion is inevitable.

[morzh]

Which pretty much means that all those baby grands, 70, 90 and such will suffer from the same problem.

[Ron Ramirez]

That is true only of the early 70 and 90 sets without AVC. The later 70 and 90 sets with AVC use a 27 triode connected as a diode for a second detector and AVC, so these will not have the distortion of the 24 power detector used in the earlier models.

[morzh]

Ron,

Why do you call it "power detector"?

Also, suppose I were to buy a 70 or 90 set to restore. How do I tell the latter from the former, is there anything on thee label or tell-tell on the chassis I could look for so I know which one's which?
Ebay has photos, but one has to know what to look for.

[Steve Davis]

Morzh, most 70s you find will be early models. You can tell an early from a late model by looking at the back of the chassis. The early model will have three IF adjustment trimmers on the left side near the tube shield, with one having a metal cover over it. The late model will have four trimmers, with the first and third having covers. The model 90 was built in three versions. The mid and late versions had AVC, only the early did not. You can also tell these at glance, the early version has a toggle switch marked normal/distant just to the left of the speaker connector. The mid and late versions do not have this switch. You can also tell a mid from a late version by counting the ganges of the tuning condenser, the late version only has three, the other two have four.

Steve

[Ron Ramirez]

Why do you call it "power detector"?

To fully answer that question, let's turn to The Radio Handbook, Editors of "Radio," copyright 1941:

The plate detector or bias detector (sometimes called a power detector) amplifies the radio-frequency wave and then rectifies it, and passes the resultant audio signal component to the succeeding audio amplifier. The detector operates on the lower bend in the plate current characteristic, because it is biased close to the cutoff point and therefore could be called a single-ended class B amplifier. The plate current is quite low in the absence of a signal, and the audio component is evidenced by an increase in the average unmodulated plate current.

Steve has already told you what to look for in model 90 sets as to which one has this "power detector" (that is, only the early models with two 45 outputs and the normal-max. toggle switch in back). And as Steve said, only the early 70 sets have the "power" detector. Later 70 models do not. These can be most easily identified by having a 35/51 RF tube, 35/51 IF tube, and 27 detector.

In nearly 40 years of restoring radios, I've only had one late version 70 cross my bench. All of the others have been early versions.

[morzh]

So we are talking about class B amp simply discarding half of the signal the way class B usually does? Not a rectification strictly speaking, but result's the same.