Re: I cut away all the old cone except for a small quarter-sized area around the voice coil area. Then I cut a slightly smaller open area on the new cone and glue it over the old one at the VC area and all around the outer ring of the metal basket. They sound quite good and last.

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That is amazing! I wish I could watch you work as I'm sure I could learn much. I'm pretty tired now after working in the garden so I think I will give radio restoration a rest for the time being. I will look for everyone on Monday. Have a great weekend!

Work resumes on the crack house radio after much frustration, lost time, and unnecessary removal of the speaker mounting bracket. I just assumed (wrong) that since I was able to retrofit the 4 x 6 speaker with the 66X1, the 4" round speakers would likewise be workable with the RCA 56X series. The major difference is the distance between chassis and the dial scale with the 66X1 being taller. Consequently, the speaker mounts higher up and it's flared basket wall does not hit the chassis.

Rather than fashion a completely new unified bracket, I was able to use a couple corner braces. Miraculously, two of four corner brace holes lined up with existing chassis holes and I only had to drill two new ones. Apparently before they started spot welding, speaker brackets were attached using self tapping screws. Then where the speaker attaches to the corner braces, I had to file the holes making them elongated adjustable slots.

As for the speaker, I went the clear spray route with a couple toilet paper patches. One covering a rectangular tear and the other a hole. Unfortunately, some of the spray ran through the felt voice coil cover and down around the magnet. Something like that can ruin your whole day. To fix that problem, I had to peel off the felt VC cover, spray WD40 to thin the clear coat, and then work the cone evey so often to prevent it from sticking. When I move the cone, I hear a scrapping noise. The speaker is probably completely ruined. I'll have to test it to see what happens.

Well... all is never lost.
You can send it off to Hank Brazeal in Alabama to be professionally re-coned... and have it come back "like new".

Hank Brazeal
Speaker Reconing & Field Coil Rewinding. Hank is the best. He is very busy. Don't waste his time. He's well into his eighties... and still going strong.. but hey.. y'never know.... so hurry-up... and be nice. He's a real gentleman.
Call him in Alabama
(205) 403 6243, E-mail hankspkr@charter.net

.. or you can measure the diameter and try to find one on ebay or here in the classifieds.
Or go to "play things of the past" ... Gary's got everything you could ever hope for there used.
http://www.oldradioparts.com/
I have drawers filled with speakers like that of every sort that I bought here and there whenever I saw them on ebay.

You'll find one.. don't sweat it.

I think Hank does the best work... probably about $30. But it will be better than when it left the factory!

That looks similar to the P-A600 from AES for $8.95, although those are mounted by the rim not the magnet.
Don

Thanks for the information. I sent an email with regard to re-coning.

Robert, you can also PM Ken G a forum member that has done several speakers for me. He does a nice job. PS, we are not related!

Jerry

The chassis is finally ready for new wiring, resistors, coupling caps, and electrolytics. Work today included mounting six new tube sockets, two rebuilt IF transformers, tuning capacitor with new grommets, tone switch, RF coil, output transformer, and volume control.

Parts from Mouser Electronics arrived today (TIP50, LR8N3, 1N4007) so next, I think I will devote some time to the power supply regulator and etched board design. The 35Z5 is right at the end of the chassis where there is plenty of room so hoping to fit the board right over the socket pins. The socket pins can act as a mounting platform and interface the board to point-to-point wiring. The hole in the middle of the socket can lead to an above chassis 150 ohm power resistor @ 5 watts since I plan on using a 50L6 rather than 35L6.

You said: "The hole in the middle of the socket can lead to an above chassis 150 ohm power resistor @ 5 watts since I plan on using a 50L6 rather than 35L6."

... but ....Why would you need a resistor if you plan on replacing a 35L6 with a 50L6?

You can just plug that 50L6 right into the 35L6 socket without any worry.
The filament string is already a bit high due to today's line voltage of 125vac compared to 110-115vac back when this radio was made.... so if anything it will take up that extra voltage just nicely.

The set will be easier to wire if the new socket keyways are pointing the same way as the originals. You posted a picture of the old sockets on the chassis, you can see the keyways on that picture. In the RF and IF stages, they set the sockets so plate and grid wires won't have to cross over, for stable operation.
Don

Well, the 35Z5 will be gone. I want to replace the 35L6 with 50L6 so I only have 22 volts excess in the series string rather than 35. That makes it 150 ohms @ 3.3W rather than 220 ohms @ 5W if the 35L6 was kept. It would be just preference because I favor the cooler running resistor. The line voltage here is 120 - 121 so I'm using that figure. Also rounding to the closest standard resistor value.

Yes, thank you. I marked the keyways on the tube layout chart prior to drilling the rivets and removing the old wafer sockets. The new sockets are placed the same as the old. The new ones also have four convenient ground lugs spaced around the mounting ring. So. I won't have to do any pin 1 to chassis soldering.

Oh yeah.. forgot you're pulling out the 35z5.
Well in that case there's even an easier perfect solution... no heat too.

Leave the 35L6 in there... go ahead and remove the 35z5... now your filament string will need only about 85v... right?
So just add a 1N4007 diode in the beginning of the filament string.
It will act as a 1/2wave rectifier producing raw-pulsating DC (to the filaments only) at an approximate equivalent/effective voltage of 84volts.
Done!

This is also a very typical fix often-used for older 4-tube radios that required 85V filaments.. and they used a line-cord (curtain-burner) resistor to drop the AC down to 85v.

The diode is probably your best easiest and least costly solution... however for your edification, there is yet another choice too...
That would be the implementation of a non-polarized AC "Dropper Capacitor" of 4.5uf rated @200vAC or 350vDC.
You can place it in series with the filaments in the beginning of the filament string along with a 20 ohm 1-watt surge resistor.
The dropper cap has the advantage of dropping the voltage but causes no heat.... just like the 1/2 wave diode solution.
Both do the job with no heat.

Here's a tutorial on it: with an Excel spreadsheet tool you can download at the very bottom of the article:
http://www.vintage-radio.com/repair-res ... calcs.html

Re: Silicon diode in series with a dropping resistor

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I still come up with a cooler series resistor (150 ohms 3.3W) by substituting 50L6 for 35L6.

Why are you saying "with a dropping resistor"???
I am confused by what you are saying...

I think you are confusing a "Capacitor" Dropper that does use a surge resistor.....
.. with a "Diode"-dropper that does not need a resistor.

If you simply use a single diode in the filament string... you will NOT need any kind of additional dropping resistor.

You are removing a 35z5 .. right?

So your remaining filament string is 12.6 + 12.6+ 12.6 + 12.6 + 35L6 = 85 volts total

If you place a 1N4007 diode in series with the filament string .... the 1/2 wave raw pulsating DC will be 84 Volts (effectively).
So you do not need to add a dropping resistor.

Re: Why are you saying "with a dropping resistor"???

==============================

The terminology came from language used on the UK link you provided. Keep in mind that when they say "Mains" they're taking about 220 volts, not 120 volts. The addition of the diode is probably a good scheme for the UK so they won't have to use a 220 to 110 step-down transformer to use an American built radio. If what they say in the text is true, the diode concept would reduce the power by half and the tubes would "think" they're on 110 volts rather than the European 220. Using the diode idea to compensate for the 35Z5 removal won't work because the whole string uses 18 watts and the 35Z5 uses just 5.25W of that total amount. In my estimation, the 50% reduction provided by the diode will not afford the remaining tubes the 12.45 watts of energy they require. However, this seems to go against the results of the formula shown on the spreadsheet. I'll have to hot wire this idea to see what happens.

Here are the test results:

Typical voltages across pins 2 & 7, all tubes light normally.
35L6 > 12SK7 > 12SK7 > 12SK7 > 12SK7 > 35L6 > 120 VAC

Series string with addition of diode.
35L6 > 12SK7 > 12SK7 > 12SK7 > 12SK7 > 35L6 > 1A Diode > 120 VAC
18.05 . 7.44 .... 7.01 ... 7.37 .... 7.79 .. 18.94

Series string with one 35 volt tube removed. (35Z5)
12SK7 > 12SK7 > 12SK7 > 12SK7 > 35L6 > 1A Diode > 120 VAC
9.67 .... 10.20 .. 10.15 .. 10.64 .. 26.15

As can be seen in test 3 of 3, the introduction of the series diode does not allow sufficient power since we operate on 110-120 volts and the UK standard is 220 volts. Voltage readings were taken using the AC mode even though it's actually pulsating DC. Therefore, reading may be skewed somewhat. However to the eye, tube filaments were glowing noticeably dimmer.

You cannot measure the voltages that way.... because it is pulsating DC...
Your volt meter will not respond properly on the DC scale and certainly not on the AC scale either.

That's why I took the time and pointed out 84 volts ( effectively)

The 1/2 wave diode does not create a 50% reduction.
There is only a 30% reduction in voltage 84/120 = 70%

( a typical quickie scientific test is to heat a (given resistor say 10k) with the pulsating DC and then measure the exact temperature with a digital thermometer..
.... and compare it with either 84 volts DC or 84 volts RMS AC )
The amount of energy expended will be the same.
A 1/2 wave rectifier fed with 120v AC == WILL create raw pulsating DC with an approximate effective 84 volts.

Don't worry about trying to measure the individual drops across each tube or the wattage.
BELIEVE me .... it is a scientific fact... the raw-pulsating DC will be a perfect EFFECTIVE 84v DC.
And those 5 tubes requiring a total of 85 volts will run just fine on it.

Yes, pulsating DC makes a world of difference so all my reading were totally bogus. I've just repeated the experiment and allowed ample time for 48 + 35 + Diode to come up to operating temperature. I also switched the lights off to observe the 35L6 glass tube and touch the 12 volt metal tubes. You are without a doubt absolutely correct. The half duty cycle provided by the diode does the job and no waste heat. Totally awesome!

So, it looks like the chassis under construction will have a 1N4007 in the filament string (at the 35Z5 end) and the voltage regulator with pass transistor providing B+. This is going to be one sweet build.

And as always, thanks for your timely and informative posts.

The crack house radio remains unfinished. I just have not been in the mood to work on it. As for the speaker disaster while attempting cone repair, I'm watching eBay for another piece of junk. Maybe I'll get lucky.

Also, someone sent me a spare loop antenna. Someday I'll glue it back together. But many thanks to the kind person and your generosity.

Crack House Radio Update: Work has not yet resumed since the radio I normally listen to developed trouble and needed attention. It was making a lot of noise with volume shifting up & down and the pilot bulb flickering. As turned out, the lead of a tubular ceramic cap was intermittently touching the lead of a resistor thanks to the assembly line skipping a little piece of lead insulating tubing. It was very hard to locate since the noise only happened briefly at random times and was causing an intermediate short between 12SQ7 detector plate and AF amp grid. Finally found it by flipping the chassis over and looking with an LED flashlight at a different angle.

As for the Crack House Radio, I've decided to change the chassis design from the original with the 12J5 oscillator to that of the 9X641 that forgoes the 12J5 and includes a 12SK7 RF amplifier. So, I'll be putting the 9X641 circuit into a 56X2 cabinet. Sweet! Needless to say, the AA6 having an RF amplifier rather than the converter as the first stage far outperforms it's less sophisticated cousin.