[Dave Slusarczyk]

Morning Guys!

I am a 20's guy and usually play over at ARF and rarely venture over here---till now.

I recently aquired a model 38-690 and it has been expertly restored by a previous owner. I am satisfied with its performance other than the volume of the tweeters. I have performed the mod that Ron had suggested and yes it has improved their performance but I am still a little unimpressed. I have to place my ear 4-6" away to hear if they are operating.

Is this typical for the speakers? Maybee I am expecting too much from them?

Secondly--how much of an improvenment will be gained by installing the back cover?? I will have to make one as mine was missing when purchased.

Thanks! Look forward to hearing back from you Philco guys!

Dave

[Syl]

I have to place my ear 4-6" away to hear if they are operating.

Maybe your hearing is at fault ?

Just a thought..

Syl

[Dave Slusarczyk]

I have to place my ear 4-6" away to hear if they are operating.

Maybe your hearing is at fault ?

Just a thought..

Syl

Thanks Syl but I feel my hearing is quite good. I will however get the wife to listen to them. Even after many years of my head being under and over operating jet engines they work quite well.

Hold on ---my wife is yelling something I did not hear her--gotta go

Dave

[Syl]

I have to place my ear 4-6" away to hear if they are operating.

Maybe your hearing is at fault ?

Just a thought..

Syl

Thanks Syl but I feel my hearing is quite good. I will however get the wife to listen to them. Even after many years of my head being under and over operating jet engines they work quite well.

Hold on ---my wife is yelling something I did not hear her--gotta go

Dave

Glad you got the humour.

Dunno about those tweeters. It could be numbers of things. Too stiff and they become unefficient ? Weak magnets ?

BTW, not hearing your wife yelling _may_ be a blessing sometimes...

Syl

[Ron Ramirez]

Hi Dave - and welcome!

I would seriously consider changing the value of capacitor (151) to 4.7 uF, non-polarized. This should help the performance of the tweeters by lowering the crossover frequency to around 4000 cycles, permitting more of the midrange audio frequencies to be reproduced by the tweeters, as well as the high end.

This is detailed, as you know, on this page on my website:
ERROR in Philco Model 38-690 Tweeter Wiring

The tweeters should not be really loud in a 38-690 - they should be noticeable, but not overpowering. This is unlike the 37-690, the tweeters of which are really TOO loud.

As for the back cover. The use of a back should make the passive radiators operate more efficiently. However, the original back had ventilation holes all the way down - which was necessary, since most of the heat was generated by the lower chassis (audio amp and power supply). The unsealed back would thus, theoretically at least, defeat the purpose of the radiators. Nevertheless, I've owned such receivers in the past (wish I still had one now...long story), and when I listened closely to one of the radiators, I could always hear sound coming from it, even though the set had no back, or a ventilated back.

[wonderwrench]

How do you have the treble/bandwidth control set? You need wide bandwidth to get high frequencies.

What are you using for source material? If your listening to just AM broadcast stations the tweeters will not see much use because most AM broadcast stations these days have very limited frequency response. Their frequency response does not go much past 5 kHz. Back in the day AM broadcast stations went to 10 KHz or more. In the case of WLW in the late 50's and into the 60's 20+ KHz.

If you really want to hear what your 690 can do build a SSTran AM transmitter. http://www.sstran.com/index.html

I built one for my father and he has a 37-690. With good source material the tweeters are noticeable.

Keep in mind a paper tweeter will never perform like a horn, dome or ribbon tweeter as they will roll off big time on the top end. I would guess they are good to 10-15 kHz.

edit: Ron I missed your post as I was working on mine at the time. I agree the tweeters get kind of bright with the bandwidth set full wide on my fathers 37-690. Any chance of popping the tweeters by dropping the crossover point down to 4000 hz on Dave's 38-690?

[Ron Ramirez]

I doubt that there would be anything to worry about at 4 kc. I would be hesitant to drop it much below that, however. But, as with all internet "advice," remember, YMMV.

The Philco "tweeters" were six inch, paper cone, drivers with small voice coils and small field coils so, as you have pointed out, their frequency response would be rather limited anyway. Add the 10 kc filter in the radio itself, and there you go...the radio is not going to reproduce above 10 kc anyway.

[Dave Slusarczyk]

Thank you very much guys. I am begining to beleive mine is performing as well as to be expected. I guess overall I am a little dissapointed. This is my first high count set and had thought I would see a big difference comared to my other consoles of lower tube count.
It is quite selective and does play quite loud. I was expecting a BOOMING bass and very noticeable high notes.


Thanks guys!

Dave

[wonderwrench]

I doubt that there would be anything to worry about at 4 kc. I would be hesitant to drop it much below that, however. But, as with all internet "advice," remember, YMMV.

The Philco "tweeters" were six inch, paper cone, drivers with small voice coils and small field coils so, as you have pointed out, their frequency response would be rather limited anyway. Add the 10 kc filter in the radio itself, and there you go...the radio is not going to reproduce above 10 kc anyway.

Are you speaking of a whistle filter? circuit location?

[Ron Ramirez]

Hi Dave

A properly restored 38-690 should deliver deep bass and noticeable treble - with the bass control set to max, and the Fidelity-Selectivity control set to maximum fidelity.

And, yes, a properly restored 38-690 will, most definitely, put any lower tube count set to shame, without a doubt.

I've owned one in the past...and had a few pass through here as repair jobs...so I know how they should sound; quite simply, SUPERB.

[Ron Ramirez]

The 37-690 and 38-690 both have filters which limit the top end audio response to 10 kc. The filter in the 37-690 is adjustable; the 1938 version is not.

The original intent of the filter was, indeed, as a "whistle" filter; to prevent adjacent channel interference. The filter is in the audio section, though; the best way to prevent adjacent channel interference is to limit the bandwidth. This is what the Fidelity-Selectivity control would do.

In addition, there is one bakelite block in the upper chassis of the 38-690. That bakelite block is NOT a capacitor!!! Instead, it contains the coils for the set's 10 kc filter.

[Dave Slusarczyk]

Hi Dave

A properly restored 38-690 should deliver deep bass and noticeable treble - with the bass control set to max, and the Fidelity-Selectivity control set to maximum fidelity.

And, yes, a properly restored 38-690 will, most definitely, put any lower tube count set to shame, without a doubt.

I've owned one in the past...and had a few pass through here as repair jobs...so I know how they should sound; quite simply, SUPERB.

Thanks Ron,

I wish I had one to compare it to. If I turn the bass up all the way up and the treble all the way it does sound good. I just never thought one would typically play set with both adj to max.


Thanks Ron,
Dave

[BDM]

How does it sound over all? How were you expecting it to sound? I've heard one, only one high fidelity set in my life. Back in 94, I was over a gents house purchasing HAM equipment. While in his front room, I noticed a very nice, and different console. I asked what it was, and he said a Philco 37-690. The radio itself was absolutely gorgeous. He told me he had restored it from the ground up. I didn't doubt him as he restored boat anchors, vintage & modern HAM transceivers as a business. He turned it on and started showing me the better aspects of the set. I remember CFCO was playing, and the sound quality was outstanding. I didn't own anything that sounded as good or as loud in the BCB. Heck I never knew Philco or any manufacture produced so called high fidelity sets until then. Tweeters, variable band width. I was intrigued.

[wonderwrench]

Hi Dave

A properly restored 38-690 should deliver deep bass and noticeable treble - with the bass control set to max, and the Fidelity-Selectivity control set to maximum fidelity.

And, yes, a properly restored 38-690 will, most definitely, put any lower tube count set to shame, without a doubt.

I've owned one in the past...and had a few pass through here as repair jobs...so I know how they should sound; quite simply, SUPERB.

Thanks Ron,

I wish I had one to compare it to. If I turn the bass up all the way up and the treble all the way it does sound good. I just never thought one would typically play set with both adj to max.


Thanks Ron,
Dave

Correct me if I'm wrong. Most bass and treble controls on old radios only cut bass and treble they can't add any like newer equipment does. So having both wide open should give flat response. Keep in mind a good set does boost the bass at low listening levels. Also do to the 690's design aka bass amp bass would be greatly exaggerate at low listening levels with the control cranked.

[wonderwrench]

Hi Dave - and welcome!

The tweeters should not be really loud in a 38-690 - they should be noticeable, but not overpowering. This is unlike the 37-690, the tweeters of which are really TOO loud.

Just by shear luck I read your post in my Crosley Broadcasting Corporation thread.
http://philcoradio.com/phorum/showthread.php?tid=1245
I did some research on NRSC as you suggested.
http://www.nrscstandards.org/download.as...SC-1-A.pdf

I think I found the reason why the 37-690's tweeters are so bright. AM broadcasts have preemphasis in the high frequencies. This was never done in the old days. WLW was flat 20-20 KHz. My father was an engineer at KSTP for over 40 years and they were flat to 15 KHz even after the limit was changed to 10 KHz. When he retired about 18 years ago preemphasis on AM did not yet exist. Also note receivers today are required to have deemphasis. I'd guess this is done to cut down on interference and noise.
[Image: http://i156.photobucket.com/albums/t25/w...sc/Pre.jpg]

[Image: http://i156.photobucket.com/albums/t25/w...sc/Dee.jpg]

I did some looking at the spec's on my fathers SSTran AM transmitter and it has a treble boost function. I'll have to check to see if it is enabled.
I bet it is by default and I was to dumb to know any better. It would explain the bright treble on the 37-690 when using the SSTran.


Thanks everyone, I learned many things today.