Taking the Plunge Into the WOPL 400-II Pool

[e30m3mon]

I'm finally going to get through this rebuild attempt, figuring the 3rd time's a charm!
A little background ... I bought this amp and the 2000-II new in 1980 (pic of receipt attached ... I actually found it while going through the accumulated paperwork - note the date!). They served me well for many years, until an overly loud party one night fried one channel and took that speaker with it. I never "forgave" the amp and relegated it to the closet(!). Fast forward to about 9 years ago and I decided the 400 spent enough time in solitary confinement and deserved a rebuild. I acquired all of the output driver and power transistors, 33ohm 5-watt resistors, diodes, and all new TO3 sockets....assuming the one blackened "B" fuse (I forget if it was the + or - side) was an indicator of at least one failed component. Might as well replace the whole back wall (as you say here). For the records, I believe it is a quasi-compliment design.

Naturally I did not check with any online resources to take the amp through a proper power-up procedure, aside from the DBTester and Variac, which I have used for other projects, and luckily the fuse did not blow this time ... yet I didn't have any signal come thru the output on either side. So back in the closet it went...life got busy, so it was not missed.

Fast-forward several more years - I discovered Phoenix and all this talk about this WOPL board that replaces the PL36...so 1.5 years ago I ordered one off ebay and it sat on the corner of my workbench until recently when I finally got up the nerve to assemble it with the hope to bring the 400-II back to life.

So a little about the system ... pics attached for reference and comments...I am hoping the installed transistors on the back wall are compatible with the WOPL14/20

The output transistors consist of 6 MJ21196G per channel (top 3 positions in all 4 columns) and one MJ15024G in the bottom position of each column.
The original Bias transitions were changed to TN6705A, but I have a new pair of 2N3405 transistors - in case the TN's are not compatible with the WOPL14/20.
I installed the WOPL electrolytics in the power supply
The passive components and TO3 sockets on the back wall were all replaced several years ago
Speaker Relay has been ordered from D3IMLAY / Don !

Thank you and I look forward to your insight
Al

 

[laatsch55]

The 15024's aren't really good drivers. We like RCA-410's.
The 21196's are the best ya can get. The original Bias are 2N3403, BUT a better sub is the 2N5088's in the P strap after pushing the 2N3403 out...

 

[laatsch55]

Beautiful work on the board....

 

[mlucitt]

Your work will provide substantial rewards.

 

[e30m3mon]

Thanks, Lee, but the beauty in that board is in the engineering. What a dream to assemble - and high quality parts. I was thinking the price of the parts alone would exceed the cost if I were t0 buy them at Mouser!

Speaking of which ... yes, I saw the RCA410 or SJ2741 called out in the Release Notes, but was hoping the 15024 would be acceptable. I can't seem to find either of these at Mouser or ebay. Is there another source of good/tested transistors?

 

[laatsch55]

If you PM me your address I'll send ya some...

 

[Gibsonian]

Good call Al on this project. You won't be disappointed!

 

[e30m3mon]

Food for thought ... seeing how these two drivers are no longer being manufactured, and good parts in short supply, have any other options been considered? I believe the NTE162 is a cross to the 410. Has that been tried?

 

[Gepetto]

Food for thought ... seeing how these two drivers are no longer being manufactured, and good parts in short supply, have any other options been considered? I believe the NTE162 is a cross to the 410. Has that been tried?

Yes the preferred path is install backplanes and go full comp. No parts shortages exist there

 

[mlucitt]

and good parts in short supply

Short supply? Are you kidding me? You have never seen Lee's parts drawers...
Many of us have some RCA410s because we have been converted to the fully complementary religious preference.
Actually, the RCA410 (or the rebadged version which is labeled RCA66546) almost never goes bad. They are tough and prefect for the driver position due to the lower gain specifications. We have never found anything to work as well for the quasi-comp architecture. RCA410 Datasheet below, I have never seen a datasheet for RCA66546 or its cousin RCA66430. I believe it would be the same as the RCA410.

 

[e30m3mon]

LOL! Too funny!
I've got a mental image, and he will be sending me some!

I've seen quite a bit of talk regarding the Full Comp backplane. It is intriguing, but I fear two things with that...delaying the completion of this project once again and adding more $ to this project. At this point I can almost see the light at the end of the tunnel and start listening to this amp again, but soon it will be track season here in the Northeast and then my focus will need to waiver between electronics and engines.

 

[wattsabundant]

I've learned the hard way that the RCA or Motorola drivers are the only acceptable devices used in the negative pole of each channel. The positive pole can be most anything. Converting to full comp eliminates concerns.

 

[Billboard]

Nice work, keep posting pics

 

[wattsabundant]

I

LOL! Too funny!
I've got a mental image, and he will be sending me some!

I've seen quite a bit of talk regarding the Full Comp backplane. It is intriguing, but I fear two things with that...delaying the completion of this project once again and adding more $ to this project. At this point I can almost see the light at the end of the tunnel and start listening to this amp again, but soon it will be track season here in the Northeast and then my focus will need to waiver between electronics and engines.

I've done a few conversions to full comp. You basically make the output stage look like the full comp series II. On the driver board you install the negative predriver in backwards and make a few changes to the protection circuit. I don't think I've done any since the back planes came out.

Now everybody line up to berate me for why you do that vs install the back planes. The answer is because you can and your on a budget. The only cost is the PNP transistors. It still takes hours and hours whichever way you go.

 

[mlucitt]

Anyway you convert to full complementary topology is fine.

 

[laatsch55]

I


I've done a few conversions to full comp. You basically make the output stage look like the full comp series II. On the driver board you install the negative predriver in backwards and make a few changes to the protection circuit. I don't think I've done any since the back planes came out.

Now everybody line up to berate me for why you do that vs install the back planes. The answer is because you can and your on a budget. The only cost is the PNP transistors. It still takes hours and hours whichever way you go.

Don, nobody gonna berate ya..and yes , lots of hours any direction ya go...
Before the backplanes came out I went on a TO3 socket buying spree....the GOOD ones, green and black...let me know if ya need some.

 

[George S.]

Has anyone successfully converted the first 700, let's call it the Series 1, the one that won't take the WOPL backplane boards, to full complementary? If so, was it worth the effort?

 

[laatsch55]

Has anyone successfully converted the first 700, let's call it the Series 1, the one that won't take the WOPL backplane boards, to full complementary? If so, was it worth the effort?

No reason to anymore George, a new chassis for 75.00??

 

[laatsch55]

Has anyone successfully converted the first 700, let's call it the Series 1, the one that won't take the WOPL backplane boards, to full complementary? If so, was it worth the effort?

Ed did a bunch over the years...

 

[e30m3mon]

Don, et al, You got me thinking about this full-compliment upgrade, and if I were to go that route at some point in the future, I think I'd just bite the bullet and get the WOPL Backplane kit. If it's anything as perfect as the PL14/20, I'd look forward to building and incorporating that into my chassis. Does it come with all the output transistors and all related components? I couldn't find much info on the WO website. Clicking the e "Documentation" link yields a "Runtime Error" message for me.