Soft Start Board Goof

[Paul Birkeland]

If you can't dial the driver tube voltage close to the target value, then you can be sure that the 2A3 voltages will be off, but that's not where you need to look for issues.

I'd double check the transistors, jumpers, and wiring of the new driver board to be sure everything is as it needs to be.  If changing the driver tubes doesn't remedy the issue, then it's most likely a minor wiring issue around the driver socket. 

 

[Grainger49]

Paul,

Are you saying that there can't be anything wrong in the plate choke circuit?

 

[InfernoSTi]

The PC-2 resistance is 327 ohms on the "good" amp.

The PC-2 resistance is 0 ohms on the "bad" amp.

 

[Grainger49]

John,

Zero, is not right.  But the PC-2 would still pass on the voltage to the plate if it were shorted out completely.  Did you trace the connections to the rest of the circuit and were they good? 

 

[Doc B]

Yeah that tends to indicate that something else that is in parallel with the plate choke is shorted. Check the filter cap that is in the circuit just before the plate choke and also check the solder pads and terminals where the wires connecting to the plate choke are connected at their other ends.

 

[InfernoSTi]

Sorry, Grainger, yes, here is the complete info:

With the amps off measure resistance on both plate chokes, red wire to black wire.

 

The PC-2 resistance is 327 ohms on the "good" amp.

The PC-2 resistance is 0 ohms on the "bad" amp.

Then check continuity from the lug with the black wire on PC-2 to Terminal 10 and from the lug with the red wire to Terminal 16.

I have continuity from the lug with the red wire to T16 on both amps.

I do not have continuity from the lug with the black wire on either amp to T10 BUT I do have continuity to T1 on both amps (which is what I think you were wanting me to check, actually).

John

 

[InfernoSTi]

Yeah that tends to indicate that something else that is in parallel with the plate choke is shorted. Check the filter cap that is in the circuit just before the plate choke and also check the solder pads and terminals where the wires connecting to the plate choke are connected at their other ends.

This should be interesting.  The filter cap of which you speak is on the power supply board, correct?  That is the one that is soldered onto the base of the power transformer, right?  Is there a good way to check the filter capacitor?  I'm looking at the amp and wondering how to do this....sorry to be a bit slow on this.

I will retouch the solder at T16 and T1 just to be sure there are good connections there. 

John

 

[Grainger49]

Often, but not always a "blown" cap has a rounded end.  Do any of the filter caps look odd?

 

[InfernoSTi]

All the caps look fine.  I'm going to try resoldering T16.  I sure hope that is it!

 

[Doc B]

A bad solder joint is more likely to create an open reading than a short. I would look for miswires or bridged solder pads and terminals. It seems that the power supply itself is OK as you get OK readings on the B+ supplying the small tube. You could try disconnecting the plate choke from the circuit, right at the plate choke terminals, and measuring the across the disconnected wires by themselves to see if you still read a short. If not then measure the plate choke terminals relative to the chassis and see if you measure a short.

 

[InfernoSTi]

Thanks for the help, Grainger.  I truly appreciate your help.

At this point, I don't think I'll be able to find the problem/solution.  I'm doing more harm than good taking things apart/putting them back together.  I'll be visiting off line with Doc about what to do next...

Best,
John

 

[Doc B]

Send her in and we'll get her goin'.

 

[InfernoSTi]

That's great, Doc!  I'm a bit embarrassed but after my third demo, parts are starting to wear out and I just want to get it going. 

John

 

[InfernoSTi]

The fine folks at BH Headquarters got my problem mono block up and running in no time flat!  

Thanks so much and I'm really excited to get them in the system and burned in...they sounded great right off the bat, just more clarity in the midrange and the upper end sounds so natural and real...the changes were noticeable right away.

Thanks again to the Bottlehead Team!

Best,
John

 

[4krow]

"They shoot Quickies, don't they?" Movie reference...I am near the end of the quickie wiring, so I won't be afraid if something goes amiss. There competent amoung us, for a price. I'll keep ya posted...hmmm, rimes with toasted.

 

[ebag4]

The fine folks at BH Headquarters got my problem mono block up and running in no time flat! 

Thanks so much and I'm really excited to get them in the system and burned in...they sounded great right off the bat, just more clarity in the midrange and the upper end sounds so natural and real...the changes were noticeable right away.

Thanks again to the Bottlehead Team!

Best,
John

Happy to hear it John, that is one KICK A$$ system you have put together.  Look out, the next time I am in your area I am looking you up, have to hear this beast of a system!

Best,
Ed

 

[jrebman]

Wow, John and Ed making a rare appearance!

Hope you guys are doing well -- we just moved (or more accurately, are in the process of unpacking) so things are a bit crazy here.

-- Jim

 

[InfernoSTi]

Greg, sounds like you are having WAY too much fun with that Quickie build! 

Ed, thank you so much for the kind words.  The BH Paramounts/HA Reference combo has me in music heaven!  You are always welcome to come by next time you are in the Austin/San Antonio area!

Jim, congratulations on the move...how exciting is that?  Sure it is a ton of work but the new place will be so nice for you and the Mrs...

Best,
John

 

[4krow]

The quickie build is getting a little weird. Just cuz I made some changes that I can't verify until the switch is thrown. Then there is the box. Yup, couldn't help myself, and now I'm up to my ass in compound angles. Pray for me.