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Stephen's WOPL Build
- Thread starter laatsch55
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Lee,
There were a number of revisions made to the PL20 pc boards Phase Linear used in the 700B. The sequence (or should I say revisions) Phase Linear made to some of their pc boards (including the PL14 and PL20 pc boards) did not always following a logical progression. One might expect that the progression would have been "PL20" then "PL20A" and then "PL20B". This was not the case among the PL20 PC boards used in the 700B and the PL14's used in their 400 series 1 amps (i.e. PL14, "universal" PL14A and the PL14B) . The sequence in which Phase Linear made the PL20 series of boards is confusing! I had always thought that the progression was: "PL20A" then the "PL20B" and then the "PL20" (and that the same goes for the PL14's). However one of the "PL20A" pc boards has the 130 ohm resistor (part of a protection circuit RC network) installed on the top side of the PC board and the capacitor was tacked (soldered) on the bottom (foil) side. So maybe the progression was PL20B, PL20A and then PL20? I will need to double-check this with Dean.
The most current version of the "PL20" had the 700B protection circuit modification included in the PC board layout and the parts (130 ohm resistor and .005/.0047 capacitor) mounted on the top side of the pc board. The earlier "PL20" initially did not have the RC network at all. A service bulletin was issued the 21st week of 1977. At which point in time Phase Linear began to installed the RC network on the foil side of the PC board like the one you show in your photo.
(NOTE: This service bulletin was later included with the 2/81 revision to the 700/700B service manual).
SERVICE BULLETIN #7721
Subject: 700B protection circuit
During the protection circuit test (page 15, step #8 of 700(B) Service Manual Rev 6/76) some 700B amplifiers may exhibit severe high-frequency oscillation in the short-circuit mode, often accompanied by the opening of the negative supply fuse. Any 700B which exhibits this problem should be modified as follows:
1) Desolder C17 (.05 mf ceramic) and discard.
2) Obtain a 130/1/2 watt resistor and a .005/100 v. capacitor.
3) Solder the series RC network across the base-collector junction of Q9 (2N1305) foil side of the PC board as shown in the diagram below.
4) Perform the protection circuit test again and verify the proper operation of the modified protection circuit.
Note: 700B's with serial number greater than 4250 contain the above modification already.
It if unfortunate that Phase Linear did not publish this same service bulletin (or include it in the service manual) for the 400 series 1 amplifier.
The "universal" PL14A pc board could be used in either the 400 or 700B. There are some slight differences, however. The differences are the 40412V1 used in the 700B application was replaced by a 40327 when used in a 400. Other differences included some resistor changes.
SIDE NOTE: The Phase Linear 700B began its initial production with a "universal" PL14A PC board (approx. 4-3/4" x 5-1/4") in the summer of 1973 (if my memory serves me correct). This evolved into the PL14B in May 1974 (with the larger format PC board 5-1/4" x 6-3/4" like that of the later PL20 series pc boards). The PL14B used in the 700B was only in production for a short while (maybe a few months?). It was then replaced by the first generation of PL20 pc boards. NOTE: The PL14B used in the 400 series 1 is a smaller format (4-3/4" x 5-1/4") PC board.
NOTE: I always perform the short circuit test on the amplifiers I repair, build or sell. This is to ensure that the protection circuit is:
1.) operating properly,
2.) weed out any weak or defective output transistors,
3.) Ensure that there are no oscillations.
I know many people out there are afraid to perform this test. However it must be performed in order for anyone to claim compliance to the manufacturer's specifications as is called out for in their service manual "Test (And Alignment) Procedures".
Ed
There were a number of revisions made to the PL20 pc boards Phase Linear used in the 700B. The sequence (or should I say revisions) Phase Linear made to some of their pc boards (including the PL14 and PL20 pc boards) did not always following a logical progression. One might expect that the progression would have been "PL20" then "PL20A" and then "PL20B". This was not the case among the PL20 PC boards used in the 700B and the PL14's used in their 400 series 1 amps (i.e. PL14, "universal" PL14A and the PL14B) . The sequence in which Phase Linear made the PL20 series of boards is confusing! I had always thought that the progression was: "PL20A" then the "PL20B" and then the "PL20" (and that the same goes for the PL14's). However one of the "PL20A" pc boards has the 130 ohm resistor (part of a protection circuit RC network) installed on the top side of the PC board and the capacitor was tacked (soldered) on the bottom (foil) side. So maybe the progression was PL20B, PL20A and then PL20? I will need to double-check this with Dean.
The most current version of the "PL20" had the 700B protection circuit modification included in the PC board layout and the parts (130 ohm resistor and .005/.0047 capacitor) mounted on the top side of the pc board. The earlier "PL20" initially did not have the RC network at all. A service bulletin was issued the 21st week of 1977. At which point in time Phase Linear began to installed the RC network on the foil side of the PC board like the one you show in your photo.
(NOTE: This service bulletin was later included with the 2/81 revision to the 700/700B service manual).
SERVICE BULLETIN #7721
Subject: 700B protection circuit
During the protection circuit test (page 15, step #8 of 700(B) Service Manual Rev 6/76) some 700B amplifiers may exhibit severe high-frequency oscillation in the short-circuit mode, often accompanied by the opening of the negative supply fuse. Any 700B which exhibits this problem should be modified as follows:
1) Desolder C17 (.05 mf ceramic) and discard.
2) Obtain a 130/1/2 watt resistor and a .005/100 v. capacitor.
3) Solder the series RC network across the base-collector junction of Q9 (2N1305) foil side of the PC board as shown in the diagram below.
4) Perform the protection circuit test again and verify the proper operation of the modified protection circuit.
Note: 700B's with serial number greater than 4250 contain the above modification already.
It if unfortunate that Phase Linear did not publish this same service bulletin (or include it in the service manual) for the 400 series 1 amplifier.
The "universal" PL14A pc board could be used in either the 400 or 700B. There are some slight differences, however. The differences are the 40412V1 used in the 700B application was replaced by a 40327 when used in a 400. Other differences included some resistor changes.
SIDE NOTE: The Phase Linear 700B began its initial production with a "universal" PL14A PC board (approx. 4-3/4" x 5-1/4") in the summer of 1973 (if my memory serves me correct). This evolved into the PL14B in May 1974 (with the larger format PC board 5-1/4" x 6-3/4" like that of the later PL20 series pc boards). The PL14B used in the 700B was only in production for a short while (maybe a few months?). It was then replaced by the first generation of PL20 pc boards. NOTE: The PL14B used in the 400 series 1 is a smaller format (4-3/4" x 5-1/4") PC board.
NOTE: I always perform the short circuit test on the amplifiers I repair, build or sell. This is to ensure that the protection circuit is:
1.) operating properly,
2.) weed out any weak or defective output transistors,
3.) Ensure that there are no oscillations.
I know many people out there are afraid to perform this test. However it must be performed in order for anyone to claim compliance to the manufacturer's specifications as is called out for in their service manual "Test (And Alignment) Procedures".
Ed
Last edited:
Some very useful info there Ed. It will be an asset to the community to pin all of the board revisions down.
I guess that is what happens to a small/medium sized company in the 70s. Perhaps they were growing too fast.
I can see how this happened, if I owned a company that was producing a product, I would want improvements or fixes implemented immediately and not wait for the next model revision. I think I would keep the revision the revision numbering in order.
I guess that is what happens to a small/medium sized company in the 70s. Perhaps they were growing too fast.
I can see how this happened, if I owned a company that was producing a product, I would want improvements or fixes implemented immediately and not wait for the next model revision. I think I would keep the revision the revision numbering in order.
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- Joined
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- 74,877
- Location
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- Tagline
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- Joined
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- Halfbiass...Electron Herder and Backass Woof
Converted to PDF ... no forced resizing. So this is your dinky JPG simply converted to the portable document format.
View attachment test.pdf
If you want to test it out further. Use Windows Scan again and up the DPI setting to 300 and then try and upload that file.
The original JPG looks very small in terms of bytes.
Microsoft 'Print to PDF' is a good way to convert stuff like this too if you don't have PDF writer/creator software on your puter.
PDF's always upload nicely through Vbulletin.
* * *
Yeah, I think it's a simple matter of the image file being too small to begin with.
Windows Scan defaults to low DPI settings. 100 DPI by default. Because it's a s s !
Force it to scan at 300 and you'll see the image file coming out much bigger ... and then it will upload in a usable size.
Vbulletin will apply a shrink to moderately big images or completely choke if the file is huge.
What Vbulletin doesn't do is scale small images "up" like your picture viewer will do inherently on it's own.
That's why you see the file big when you view it on your puter before you try uploading it to the site.
Vbulletin is just TOO literal when it comes to image handling.
View attachment test.pdf
If you want to test it out further. Use Windows Scan again and up the DPI setting to 300 and then try and upload that file.
The original JPG looks very small in terms of bytes.
Microsoft 'Print to PDF' is a good way to convert stuff like this too if you don't have PDF writer/creator software on your puter.
PDF's always upload nicely through Vbulletin.
* * *
Yeah, I think it's a simple matter of the image file being too small to begin with.
Windows Scan defaults to low DPI settings. 100 DPI by default. Because it's a s s !
Force it to scan at 300 and you'll see the image file coming out much bigger ... and then it will upload in a usable size.
Vbulletin will apply a shrink to moderately big images or completely choke if the file is huge.
What Vbulletin doesn't do is scale small images "up" like your picture viewer will do inherently on it's own.
That's why you see the file big when you view it on your puter before you try uploading it to the site.
Vbulletin is just TOO literal when it comes to image handling.
Last edited:
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Thanks Lee. I'd like to know about your analyzer. I've read through old threads, but have not seen the make & model.
Also, your 'load cell' Pretty impressive! What is inside? All I have so far is a couple 100 watt 8 ohm Dale power resistors. Watching for more on the bay for a good price to stack up.
I thought I read where you had some power resistors in a bucket of water at one time? Maybe I'm getting lost in a sea of info here.
Again, thanks for the pictures.
Brad
Oh; Do you keep all of the 'original' PL circuit boards from your WOPL builds? Could make an interesting display of the variations over the years.
Also, your 'load cell' Pretty impressive! What is inside? All I have so far is a couple 100 watt 8 ohm Dale power resistors. Watching for more on the bay for a good price to stack up.
I thought I read where you had some power resistors in a bucket of water at one time? Maybe I'm getting lost in a sea of info here.
Again, thanks for the pictures.
Brad
Oh; Do you keep all of the 'original' PL circuit boards from your WOPL builds? Could make an interesting display of the variations over the years.
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![DSCN0609[1].jpg](/data/attachments/27/27551-d6c56b54cf56e295685c7af49c2b2793.jpg)
![DSCN0610[1].jpg](/data/attachments/27/27552-1e1b654b6765a3a21ab0853e5140043b.jpg)
- Joined
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![DSCN0612[1].jpg](/data/attachments/27/27553-b016b109d072d291bd7478ae5b53efa4.jpg)