David's Phase Linear 700B Thread

Phase Linear Phanatic

Phase Linear Phanatic

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Gepetto said:
Check for blown small signal diodes especially in location D9 and D12. If the meter pegged with the negative outputs shorted in the -20dB position it could take out these diodes (doubful but worth checking)
Click to expand...
This is exactly what I suspected happened back in 1998 when I bought it from a guy. He probably pegged the needle while the - outputs were shorted in the -20db position. It wasnt untill this year that I opened her up myself and found the wires for that switch, were wired together, heat shrunk, and the switch internals missing. I had a local vintage shop here replace that switch. But since the -20db switches are now defunct, he had to get a similar one from latvia. Regardless however.........it is worth noting to you that the meter issue has ALWAYS existed as long as I have had the amp. This assumes the old light board in place in 1998. I think the guy I bought it from stressed out the meter windings on one side when he blew out a channel. Lee said these meters are kinda crappy anyway? But are the hardest item (aside from handles) to find. So whatever controls the meter needle itself mechanically; may suspect if we have replaced all components and all boards with WOA parts? OR (sarcastically here......) its another dreaded MILA METER!! (Gasp!) :eek: :eek:
 
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Phase Linear Phanatic said:
This is exactly what I suspected happened back in 1998 when I bought it from a guy. He probably pegged the needle while the - outputs were shorted in the -20db position. It wasnt untill this year that I opened her up myself and found the wires for that switch, were wired together, heat shrunk, and the switch internals missing. I had a local vintage shop here replace that switch. But since the -20db switches are now defunct, he had to get a similar one from latvia. Regardless however.........it is worth noting to you that the meter issue has ALWAYS existed as long as I have had the amp. This assumes the old light board in place in 1998. I think the guy I bought it from stressed out the meter windings on one side when he blew out a channel. Lee said these meters are kinda crappy anyway? But are the hardest item (aside from handles) to find. So whatever controls the meter needle itself mechanically; may suspect if we have replaced all components and all boards with WOA parts? OR (sarcastically here......) its another dreaded MILA METER!! (Gasp!) :eek: :eek:
Click to expand...
Ahh, check the switch or switch wiring.

The switch has to be a DPST or DPDT to work properly in this amp. The common of both switches are wired together and to ground. The Normally Open (NO) positions on each of the 2 switches goes to PAD2 and PAD5. When the switches are open, it is in full power mode with the 22K and 1.8K ohm resistor in series to ground. When the switches are in the closed position, this is the -20dB position, each switch shorts across the 22K ohm resistors and attaches the end of the 1.8K ohm resistors to ground.

Clear?
 
Phase Linear Phanatic

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Thank You's

I just want to take a moment to thank all of you who were involved in this PLWOA 700B conversion. Lee, Joe, Jerry, Dennis (I think...:confused2:) and Nando for welcoming me to the forum in the beginning, and Skratch along with countless others who have commented and viewed this forum topic. Hopefully it was a learning experience for us all. Especially ME! :toothy10:

I hope to see you all at the next conversion!!
 
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Another Born Again Convert to PL. I like it! I bet there may be a few other members who might do the same.

Nando.
 
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Thanks Nav! Yeah, let me go get some 24 awg wire and put these bias Q's where they belong.

Now... about the meters.... Diodes are good and switch is wired and working right.

But....

Joe - if DC resistance of the coils themselves is any indication, then yeah I think I see a difference.. (no I did NOT peg 'em with the meter I'm using.. ). This is measured with one lead off, so nothing else is in circuit..

Right meter - 130 ohms
Left meter - 80 ohms

That's a pretty significant difference, isn't it? Yes I know.. 3.9k and a 1.5 volt, but I don't exactly have a 3.9K guy handy at the moment..
 
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jbeckva said:
Thanks Nav! Yeah, let me go get some 24 awg wire and put these bias Q's where they belong.

Now... about the meters.... Diodes are good and switch is wired and working right.

But....

Joe - if DC resistance of the coils themselves is any indication, then yeah I think I see a difference.. (no I did NOT peg 'em with the meter I'm using.. ). This is measured with one lead off, so nothing else is in circuit..

Right meter - 130 ohms
Left meter - 80 ohms

That's a pretty significant difference, isn't it? Yes I know.. 3.9k and a 1.5 volt, but I don't exactly have a 3.9K guy handy at the moment..
Click to expand...
Yeah that difference will do it Jer. That confirms something is wrong with the one meter. They are normally somewhere in the 70-80 ohm range.
 
Phase Linear Phanatic

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Gepetto said:
Yeah that difference will do it Jer. That confirms something is wrong with the one meter. They are normally somewhere in the 70-80 ohm range.
Click to expand...
Joe, if 70-80 is the norm, then yuppers. That explains the right meter being "bouncy", and the left more accurate with the music. If I have a bad meter.............what or HOW could I find a replacement? I think a 700B meter is more scarce than the "fabled rack handles" in a blister pack. (of which we saw there was factual evidence of.) However, the price was very high for those. And I'd assume that would be a similar case for a replacement meter if found. Grrrrr...... and we almost had it. :banghead:
 
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Almost had what?? Meters do come up from time to time on e-bay. Be prepared to spend more than 75.00, that's what the last one went for...
 
Phase Linear Phanatic

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laatsch55 said:
Almost had what?? Meters do come up from time to time on e-bay. Be prepared to spend more than 75.00, that's what the last one went for...
Click to expand...
Almost had it troubleshot down to a faulty component Lee. Was hoping it was NOT the meter itself, and just a diode or resistor. I'll keep my eyes peeled for one. $75 seems normal for that piece. All things considered, you guys have done one heck of a job getting this amps issues figured out. We are almost there. :)
 
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laatsch55

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Too bad it's not a 400, got a few of those. The only difference between them is one swings from the top and the other from the bottom.Was always gonna try and see what a bottom swingin 700 looked like...


Here's a link to almost factory replacement knobs. Put some on a couple "B"'s they looked REALLY good=------http://www.tubesandmore.com/products/knobs?sort=recommended&page=10.....Part number P-K312
 
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