[morzh]

Well,

eventually I succeeded in bringing myself to start on this one. I think I bought it in the spring. Or early summer. Anyway.

Today I pulled the chassis out, as I expected it was repaired at some point and maybe it even works (at least the seller indicated that it did) but I want to do right by this radio and am not even interested if it plays right now.

For starters I noticed that all those caps that were replaced (some tin cans and two electrolytics) were installed over the existinfg ones that were disconnected.
The backelites all stayed, even those that are Mains filters which I strongly object to.

The version I have is the two 45 tubes output one.
http://www.nostalgiaair.org/PagesByModel...013881.pdf
(the second sch in this booklet).

I have noticed this:

the schematic shows 250k resistor #33 connected to the "H" terminal of the bias wirewound resistor #38. The "J" terminal has #47 resistor going to it and it is the only one there.
In my chassis (I did verify it is what I think it is, all the tubes line-up is correct) both the 250K resistor #33 (in my case I think it is 240k by the colors) and #47 (the latter is connected by a long wire and is at the opposite side of the chassis) resistor are soldered to the "J" terminal.
The "H" terminal is empty. Better yet it looks like it has never has been soldered to, factory clean, and the "J" terminal soldering looks factory also.

Does anyone know if there are factory variations with 90 2x45 chassis?

PS. Just thought that 2x45=90.......coincidence?

[morzh]

So,

Q1: the one just asked. About the wirewound multitap resistor above.
Q2: There is the #52 inductor in the filtering circuit from the detector to the 1st Audio.I think it forms the filter with #17 cap. Both are absent.
The nductors is listed as 03086 stock #. What is it?
Q3. The #17 cap is listed as .000035mf and is 4990 stock part #. The cap #22 is listed as 0.00035 and is also 4990 stock #. How does that work?
Q4. the cap #28 is a double 2 of 0.25uFand 1 of 0.5uF. Which one goes where?
Q5: #46 cap is listed as 0.001uF (1nF). Seems to low. What I have installed by the previous owner is .022uF, and what the 2x47 tube version lists in the similar place is 10nF (0.01uF).

[morzh]

What! No one? Knows? Any-thang! C'mon, people! It's not Christmas holiday yet!

In addition to the previous yelp for help, does anyone have an original 2x45 90 chassis underbelly picture?

[Ron Ramirez]

I just arrived home from work, so I'll do what I can...

Q1. What about the wirewound multitap resistor? What exactly are you needing to know about it?
If you look at this schematic, it lists the resistance values of the various sections along with part values of the other resistors (and capacitors).

Q2. I still haven't found some of my books after moving. You can probably use a 2.5 mH RF choke to replace (52).

Q3. Both (17) and (22) should be 350 pF (0.00035 uF). The extra 0 for the cap (17) is a typo.

Q4. See the 90 schematic with two 45 tubes on my website.
http://www.philcoradio.com/tech/images/90a.jpg

Q5. Yup, the original is listed as .001 uF. I would say that the Philco engineers selected a low value as this is coming off the pi filter containing the RF choke. You are comparing apples to oranges in comparing this circuit to that of the 1-47 90 and the 2-47 90 since the later two versions used AVC and a 27 tube connected as a diode as a 2nd detector instead of a 24 tube hooked up as the infamous "power detector" (high distortion).
But I am no engineer, nor do I play one on TV.

As for the question in your last post, sorry but I no longer own a 90 with two 45 tubes. Both of my 90 chassis are 1-47.

[morzh]

Ron

Thanks, it helps.

Now to re-iterate what I wanted to ask in Q1. (I will just copy the question from the first post)

Q1. the schematic shows 250k resistor #33 connected to the "H" terminal of the bias wirewound resistor #38. The "J" terminal has #47 resistor of 13k going to it and it is the only one there.
In my chassis (I did verify it is what I think it is, all the tubes line-up is correct) both the 250K resistor #33 (in my case I think it is 240k by the colors) and the 13K #47 (the latter is connected by a long wire and is at the opposite side of the chassis) resistor are soldered to the "J" terminal.
The "H" terminal is empty. Better yet it looks like it has never has been soldered to, factory clean, and the "J" terminal soldering looks factory also.

Does anyone know if there are factory variations with 90 2x45 chassis?

Q3. The 4990 mica cap. Logic dictates that it is a typo, yes, and both values should be the same. You list the 350pF (0.00035uF). Now Chuck's website lists the same capacitor as 35pF.

Part No. Capacity mmf. (pf.) Type Color Code
4990 35 2 or 3 Green yellow

http://www.philcorepairbench.com/micacap.htm

So, are both of them 350pF or 35pF? The ultimate answer would be "this value comes from the chassis", as the documentation, as we see often, contains typos.

I think it will benefit all of us if we could figure this out; if Chuck's info is incorrect he could use the correct info then.

Q5.1. (in addition to the Q5): The underbelly diagram shows that #46 cap as a backelite block cap, which is absent in my chassis. The part number 5215 however, according to the same Chuck's information on micas, lists the cap as a mica of 1000pF.

http://www.philcorepairbench.com/micacap.htm

Part No. Capacity mmf. (pf.) Type Color Code
5215 1,000 3 Green White

This is why I was asking about the underbelly photos, if anyone has them for the 2x45 chassis.

In any case, I think a micamold here is unnecessary as this cap can be a simple film cap, it is not any longer a tuned circuit. What do you think?


Again, thanks.

[Ron Ramirez]

Q1. I am not aware of any production changes in the early (2-45) Model 90. I would guess that whoever removed the RF choke and one of the caps from that 2nd detector filter network also miswired resistors (33) and (47). I don't have a 2-45 90 to compare.

Q3. Since I still have not unpacked all of my material, I am going to defer to Chuck who, I am sure, will chime in here within the next 24 hours. If my info is incorrect (and it may very well be), I'll have to correct it.

Q5. Again, I am going to defer to Chuck, same reason (material still packed up).

[morzh]

http://philcoradio.com/phorum/showthread...=PHilco+90

I actually found one more mistake: remember this thread? There was that capacitor, with no position number next to resistor #47, which could not be found, and the questioned connection of it to GND?

The schematic here on Philco Phorum is still showing that, don't know if Chuck corrected his version yet.

Here's how it is: this cap is indeed non-existent, and the guess was correct, the lower contact of the left coil of the transformer #13 should go to the "D" voltage, where it is decoupled by the cap #29 to the "C" (rect. negative). There should be a dot there where the no-name cap upper lead crosses "D" line and the cap itself should be removed.

Here's the answer: the

[morzh]

Well, the thread is getting stale so I am just adding a string to keep it fresh.
Chuck and Ron, I hope you guys could resolve that cap value mystery as well as correct the schematics.

[Ron Ramirez]

Okay, mystery cap removed.

http://www.philcoradio.com/tech/images/90a.jpg

Now, since you own a 90 with dual 45 outputs (and I don't), you are saying that your 90 did not have the "mystery" cap in it? I just wanted to confirm that point. It actually made sense to me that there would be a plate bypass cap along the B+ line which feeds the plates of the RF, 1st det. and IF tubes. But if it isn't there, then it shouldn't be on the schematic...

[morzh]

Ron

As I said, it IS in fact bypassed by the #29 cap to the "C" node. The readability of the schematic of course is not aided by putting a node in several places and then showing a decoupling cap in one of them, but then it is there.
It gets even better: while #29 is shown in the sch as a bypass for the output, it is physicall located at the coil #13 where the mystery cap is shown. But then it bypasses to "C" and not to the chassis which would make sense for the RF stages.
The output stage in turn has no decoupling other than the electrolytic capacitor (the #29 is in parallel to it).

The point of the correction is not just removing the cap from the sch (it is still there BTW when I went to the link above) but connecting the lower pin of the coil #13 (the one that is connected to the caps #11 and #12) to the "D" node. And removing that cap to the right of the resistor #47. Otherwise as you see we do not have the plate voltage connected to that coil (which is the load). And then the same "D" node is decoupled to the "C" by the #29 cap which is 0.05uF.

As for the mystery cap itself, the first time the question was raised in the thread the link of which I put above and obviously the cap was not there either. Could be a Philco wish list item. We even discussed a possible value then. It probably would not be a bad idea to put it there, of course having connected it to the "D" terminal.

[Ron Ramirez]

Go to the link again and hit "refresh" in your browser. Or clear your browser's cache and then view the schematic again - it is indeed fixed.

[morzh]

PS. I wrote to Scott Fletcher whose thread it was, asking him to look in his chassis but got no reply so far.

[Ron Ramirez]

A lot of older radios used a large value plate bypass capacitor in the B+ line feeding the plates of the front end tubes. I've been fooling around with old radios since 1974, and while I don't claim to know it all, I do know my way around a few old radios. It's been quite a while since I owned an early 90 with dual 45 outputs, so I frankly did not remember whether it had a large value plate bypass cap or not. Obviously not.

I'm off to install a ceiling light fixture in the living room. Have a nice day.

[Scott Fletcher]

Hi Morzh :
I found this thread last night and sent you a PM with some coments about how my 90 is wired. I want now to let you and Ron know several more facts that I just found looking at my notes and my chassis. Your question 5 about the #46 cap- My radio had Philco cond. block 3903-J installed which is a.01mf cap. I restuffed with this same size and the radio works well.

Also the chassis location of the two metal containers with caps. inside, numbers 28 and 25 were interchanged on my radio. This confused me briefly, along with the fact that the driver transformer for the two 45 output tubes had an open primary and had been bypassed per Ron's information on this website.

Another comment, the H terminal of the multitapped resistor, #38, does have the 250k resistor and it is connected as the sch.shows.

The #52 choke in my radio is a small plastic cylinder labeled Remler R. F. choke #35.

[morzh]

Thanks Scott.

Well, as everyone can see some info in Rider's is wrong and what's more it is confusing as heck - the chassis drawing shows a backelite, the parts list shows a mica; or better yet that 35pF - 350pF question.

As for Q3 (350pF - 35pF) I looked at a very similar detector in 70, which uses a similar Pi-filter, and the values are 500pF and 250pF so I think I will go with 350pF in mine (no, I do not know the inductance, but I went with Ron's advice and bought 2.5mH one).

I ordered parts from Mouser, and they shipped Thursday, so I hope I will get them beginning this week.

Last thing I am kinda not sure of is that 1000pF cap from detector to the 1st Audio - the 1000 pF value will have about 1.5MOhm impedance at 100Hz which is a bit large, then again, I am not really a tube specialist so I do not know off the top of my head if it is bad or not. But out of common considerations that (and I do not have a datasheet for 27 tube) that say dynamic Miller capacitance is on the order of 100pF in some amp arrangement, the DC blocking capacitance should exceed it by more than that.

Do you think your 3903-J was factory installed?