Speaker Cabinet Done

[Joseph W Strickland]

Today I finished putting together the speaker cabinet I have been working on for my 800B. I had decided to go with this approach using a custom enclosure so I could control the response of the design better. I elected to use a new 15 inch woofer, a Dayton Audio DC-380-8 and a Visaton BG13-P from Parts Express. After doing some calculations based on the capabilities of the speakers, I built a cabinet that is a bass reflex and uses a 4 inch diameter port with internal and external flares also from Parts Express. I have the external flare in place but still have to trim the port to correct internal length. I need to visit my friend to take advantage of his band saw to accurately cut that part.

Other items that still have to be done include wiring the drivers to the cross-over network and adding filler for sound deadening. I might use some polyfill as I have heard that fiberglass may cause corrosion over time. To begin with I will leave off any level controls for the mid-tweeter driver. If it turns out to need it I can still add one later.

When I have checked out the speaker with the radio tuner chassis and power supply chassis I can begin work on making a custom cabinet to place the speaker cabinet in plus a record changer.

Here is a picture:

[Joseph W Strickland]

Tom;

The same man, Larry Lindsy, gave me the Silvertone console that gave me the 800B I am restoring. He is the activities director of the Vintage Antique Radio & Phonograph Society in the Dallas-Ft. Worth area. He has a number of E H Scott receivers at home that he is restoring. He has a nice Philharmonic and was working on a couple of cabinets for some of the All-Wave receivers if I remember correctly. It is nice to see the old equipment brought back from the brink by dedicated restorers.

Joe

[Tom Jardine]

Joe,

I agree whole heartedly that it's great fun and rewarding to work on these old sets. I'm a little sorry I'm nearing the end of working on the Philharmonic. Seeing the final result of putting all correct value capacitors and resistors and doing a proper alignment makes all the work worth while. There was an interesting article in Antique Radio Classified on the Philharmonic where the author claimed an inherent design fault where the final IF became overdrivn because of ineffective AGC in the RF and IF strip. This would cause distortion at the detector/first audio stage in his test example. I did not find that on mine. The modulated RF generator signal looked fine at the volume control even with max setting of the sensitivity on my receiver. I spent a lot of time adjusting the RF, IF and Audio "diodes" which probably helped. See photo.

Tom

[Norman S Braithwaite]

Tom:

The general consensus of collectors in the know is that the IF strip of the Philharmonic featured in the referenced article was not properly aligned.

Norman

[Joseph W Strickland]

Tom;

Re. the overdriven IF stage comment on Antique Radio forum, a number of possible causes could be involved including an IF tube with grid leakage. It is always good to try known good tubes before blaming circuitry. Voltages to a tube can be off and in some cases a defective tube itself can cause voltages at that tube or others downstream from it to be off.

I see you have a Tektronix 2235 O-scope. I have a 2335 model, which is a portable type, 100mHz unit. It is great to have a scope to look at signals in radios and televisions. It will reveal some problems that a simple voltage check will not.

Yes that is a very clean sine wave, indicative of fine reception and processing of the signal.

Now all you need is a radio cabinet with glass top and upper sides so that the chassis can be viewed in all its glory!

Joe

[Joseph W Strickland]

Norman;

That explains it perfectly.

Joe

Norman S Braithwaite said:

Tom:

The general consensus of collectors in the know is that the IF strip of the Philharmonic featured in the referenced article was not properly aligned.

Norman

[Tom Jardine]

Joe,

That made me chuckle. I have a Georgian cabinet with a fixed lid over the tuner. The Chippendale Grande, a similar cabinet had a top with hinges above the tuner chassis which would be nice, especially for checking tubes!

I was at the right place at the right time years ago and acquired used test equipment from our engineering lab that was replaced by newer stuff. My heavier test equipment is in the basement, and I wasn't going to carry the Scott chassis' down there and visa versa the test equipment to the second floor. My HP 616 generator remained in the basement with the better and heavier scope. Friend and neighbor Chuck Azzalina gave me a tired old Philco RF generator which was re-capped to use and modified to bring in external modulation from my BK function generator and then monitored the gen RF output with an HP digital counter. Chuck was there when I took the picture to prove I had undistorted output of the 4th IF secondary.

Now for some reason the scratch suppressor works well on broadcast audio, but not effective on the phono input. I'm feeding the phono input from the output of a Fisher single tube preamp. I can't see what the difference would be. The input levels from the broadcast audio and phono are pretty similar. The negative bias voltage resistor strip is OK as well.

Tom

[Tom Jardine]

Norman S Braithwaite said:\

Tom:

The general consensus of collectors in the know is that the IF strip of the Philharmonic featured in the referenced article was not properly aligned.

Norman

That's what I suspected, Norman.   Tom

[Joseph W Strickland]

The Highpass 2nd order 8 ohm crossover for the mid-tweeter driver called for a 3.6uH coil and a 28uF capacitor. The closest parts I could find were a 3.5uH coil and a 20uF plus an 8.2uF set of capacitors rated at 250V from Parts Express. Their price was reasonable and the capacitors are metalized polypropylene types which will basically last forever in this type of service - no electrolytics to dry out!

I managed to get them installed in the cabinet today. I used a bakelite terminal strip to make the soldered component and wire connections. Then the parts were all bonded to the cabinet with flexible caulk. That way there should be no vibrations to cause noise. I will run a response test as soon as things have time to cure. The front port flare was also sealed using the same caulk.

The rear + and - terminals are banana jacks spaced at the standard spacing used for test equipment. That way if I choose to I can use a double banana plug at the interface. The jacks are mounted in a 3 inch circular cut-out on the back-panel so that they are recessed. I mounted them on standard 1/4 inch thick plywood. All wire connections inside are soldered.

Here is a picture of the Highpass crossover components before installation.

The rest of the resistors I ordered from Mouser Electronics came in today too, so I have all the resistors I need to finish replacing the resistors throughout the radio. I have another order coming from them that includes a large number of .1uF and .047uF 630VDC capacitors for rebuilding more of the bathtub capacitor assemblies in the radio.

Joe