[Syl]

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

Dave,

I just had a look at the link provided by Ron.

You can try connecting the tweeters (6" tweeters are more like midrange speakers to me) using a 4,7uF in parallel with the woofer. This way you'll know if the tweeters are at fault or maybe the OPT ?

Syl

[Ron Ramirez]

If you compare the schematics of the 37-690 and 38-690, you will see that the tweeters are driven by the output tubes in the 37-690, as is the woofer. This is the reason the tweeters are so loud in the 37 model. (Too loud, in my opinion; even taking the NRSC pre-emphasis curve into consideration.)

In the 38-690, the tweeters are driven by the DRIVER tube; there is a special winding in the audio interstage transformer just for the tweeter voice coils. For this reason, the tweeters are more subdued in the 38 model.

I think this was an attempt by Philco to give the tweeters just enough "presence" without being "in your face" on the high end, unlike their 37-690 model. Now, some of us do not hear the higher frequencies as well as others, so the 38-690 may seem as if its tweeters are not working, when in fact they may be working just fine (even with the phase correction I discuss on my site). Syl has pointed this out already.

I also agree with Syl when he says the tweeters in these models are more like midrange speakers. The set was not designed to reproduce audio above 10 kc, anyway.

[Syl]

If you compare the schematics of the 37-690 and 38-690, you will see that the tweeters are driven by the output tubes in the 37-690, as is the woofer. This is the reason the tweeters are so loud in the 37 model. (Too loud, in my opinion; even taking the NRSC pre-emphasis curve into consideration.

The whole problem lies in the size of the "tweeters". I agree with you on the upper limit frequency of around 10Khz. I think the Philco engineerz designed this model to be "impressive" hence the illogical size of the tweeters (one would have be sufficient AFAIK). 4" tweeters would offer a better frequency response and also be a better match to the woofer. In such a design, the engineer should have taken into account the response curve and sound pressure of the woofer then match the tweeters with a simple resistor/capacitor network, something they obviously didn't do.

Interesting that Philco adopted such a complicated solution in adding a special winding to the driver transformer instead of adding a simple resistor/cap network to the tweeters and keeping them in parallel with the woofer. I guess they were radio engineers, not audio engineers...

By looking at the schematic, a 6F6 used as a driver (equivalent to an SE amp) I figured 1-2Watts to be enough to drive both tweeters. I guessed wrong apparently. My suggestion in this case would be to add a small value power resistor (say 4ohms) in series with a 4uF cap. The whole in parallel with the _woofer_. This should do it. Idea is to match the total db level of "tweeters vs the woofer".

I would also add a small "whizzer" to the tweeters. Yeah I know, it's hot-rodding, but it is reversible and will definitely enhance the upper frequencies. I did it with my top of the line Nothern console's 12 inches -in a ported enclosure mind you- and it did a very noticeable difference (I had to recone the woofer too so it wasn't complicated to do). I have plenty of whizzers on hand so this was an easy fix, still it is pretty simple to make one using cardstock. Definitely worth it.

Just a thought.

Syl

[Dave Slusarczyk]

thanks guys,

I know have a couple of things to try. One of which is this "whizzer"? Clue me in Syl. What in Gods name is a "whizzer"?

Dave

[wonderwrench]

If you compare the schematics of the 37-690 and 38-690, you will see that the tweeters are driven by the output tubes in the 37-690, as is the woofer. This is the reason the tweeters are so loud in the 37 model. (Too loud, in my opinion; even taking the NRSC pre-emphasis curve into consideration.)

In the 38-690, the tweeters are driven by the DRIVER tube; there is a special winding in the audio interstage transformer just for the tweeter voice coils. For this reason, the tweeters are more subdued in the 38 model.

I think this was an attempt by Philco to give the tweeters just enough "presence" without being "in your face" on the high end, unlike their 37-690 model. Now, some of us do not hear the higher frequencies as well as others, so the 38-690 may seem as if its tweeters are not working, when in fact they may be working just fine (even with the phase correction I discuss on my site). Syl has pointed this out already.

I also agree with Syl when he says the tweeters in these models are more like midrange speakers. The set was not designed to reproduce audio above 10 kc, anyway.

I did notice the circuity differences. Two different ways to get the job done. Which is best I have no clue. IMO the only way to know for sure would be to compare a 37-690 and a 38-690 head to head. To do this you would need some quality source material and a quality wide band AM transmitter with a flat frequency response. If you wanted to get picky a spectrum analyzer and some good test CD's with white noise and or tone tracks.
Sounds like too much work to me.

[wonderwrench]

thanks guys,

I know have a couple of things to try. One of which is this "whizzer"? Clue me in Syl. What in Gods name is a "whizzer"?

Dave

Quote: whizzer: a small, light cone attached to the joint between the voice coil and the primary cone. The whizzer cone extends the high frequency response of the driver and broadens its high frequency directivity, which would otherwise be greatly narrowed due to the outer diameter cone material failing to keep up with the central voice coil at higher frequencies. The main cone in a whizzer design is manufactured so as to flex more in the outer diameter than in the center. The result is that the main cone delivers low frequencies and the whizzer cone contributes most of the higher frequencies. Since the whizzer cone is smaller than the main diaphragm, output dispersion at high frequencies is improved relative to an equivalent single larger diaphragm.
http://en.wikipedia.org/wiki/Loudspeaker

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

[Ron Ramirez]

IMO the only way to know for sure would be to compare a 37-690 and a 38-690 head to head. To do this you would need some quality source material and a quality wide band AM transmitter with a flat frequency response.

I've done the "unscientific" comparison of the two, using over-the-air programming. The 37-690's tweeters are too loud, IMO. The 38-690's tweeters, when the phase of the wiring is correct, are much more subtle.

[Syl]

IMO the only way to know for sure would be to compare a 37-690 and a 38-690 head to head. To do this you would need some quality source material and a quality wide band AM transmitter with a flat frequency response.

I've done the "unscientific" comparison of the two, using over-the-air programming. The 37-690's tweeters are too loud, IMO. The 38-690's tweeters, when the phase of the wiring is correct, are much more subtle.

This would be called a subjective golden ear AB test...;)

Syl

[Syl]

thanks guys,

I know have a couple of things to try. One of which is this "whizzer"? Clue me in Syl. What in Gods name is a "whizzer"?

Dave

Looks like wonderwrench beat me to it.

But his picture shows a US version of the whizzer. I prefer the French version where the center "cap" is replaced with a "béret".

Syl

[Dave Slusarczyk]

Evening guys,

Thanks for teh explanation of the "whizzer"--interesting.

I will experiment and keep you all posted.

Dave

[Syl]

Evening guys,

Thanks for teh explanation of the "whizzer"--interesting.

I will experiment and keep you all posted.

Dave

Just a note,

The whizzer could be made of something else than paper.

Using soft plastics like yogurt (polyethylene?) containers will boost high frequencies by an order of magnitude compared to paper.

Syl

[Dave Slusarczyk]

Syl,

How is it you affix the "whizzer" to the paper cone??

Thanks,
Dave

[Syl]

Syl,

How is it you affix the "whizzer" to the paper cone??

Thanks,
Dave

Hi Dave,

Elmer's carpenters glue. Spread a bead around the base of the whizzer
and affix to the perimeter of the dust cap (soft glue NOT recommended). Be sure the whizzer isn't glued to the speaker cone itself and add a small weight on the whizzer while the glue sets to create a good and uniform bond.

It's easy afterward to cut the whizzer and replace the dust cap if you ever change your mind.

Syl

[Dave Slusarczyk]

Afternoon Syl,

I am contemplating insstalling "whizzers". Can one purchase "whizzers" from a supplier?? I do not mind making my own but would prefer purchasing manufactured ones.

How about the speaker "caps"?

Thanks,
Dave

[Terry Judkins]

My 'whizzer'.

[Image: http://home.comcast.net/~suptjud/Whizzer.JPG]

A Styrofoam cup from Williamson's Brothers Barbecue... ummmm good.