[bhjazz]

Email dispatched to Hammond. I had a chat with a fellow DIYer who works on old computer displays, and he feels the transformer has failed. More soon.

Mark @ Hammond wrote back, on a Sunday night no less. He said the way I was testing it was completely wrong. Instead, he suggested to test it like this:

Red one lead, Red other lead, should be 573.5V, no load +/-2% with exactly 120V input
Green one lead, Green other lead, should be 7V, no load +/-2% with exactly 120V input
This is all you need to do but you could move one lead to each center tap and the voltage should be half.
The 50V can be check by going from the RED/EL with one lead, VIO to the other lead.

Using this testing, the transformer checks out fine. I'm crossing it off of the list.

What in the heck do you mean by "twisted red wire goes to ground" - where do those wires come from?

You sure none of the wires coming out of the transformer are damaged?

Thanks for asking, Eric. The twisted red wires in that photo go to ground. They come in from the IEC inlet. I should have made them up in green.
None of the wires from the transformer are damaged. Double checked, though.

With no power connected, can you measure resistance between the two red primaries?

Sure.
RED/RED: 233 Ohm
RED/RED-YEL: 119 Ohm

So with that in mind, I dropped the power supply board back into the case and connected it up to the transformer. Before doing so, I reheated most of the solder joints just to be sure.

At power up, I was watching to see if the EZ81 tube heaters were showing signs of life, but saw smoke again from C5. I powered it down and found that cap to be much hotter than the other 2 big caps. It also had a great fragrance!

At this point I'm going to replace all three big caps: C1, C4, C5. I'll probably do C6 as well as it is just too close to C5, both physically and in the schematic. C5 for sure is the problem cap. Jeff Rossel originally sent me three 450V 680uF caps so I'll just replace with the same value. They were Nippon Chemicon. I'm sure they were fine ten years ago when I bought them as many others here used Jeff's kits for this project. Maybe that one cap just dried out after all this time. Serves me right for waiting so long. I'm just glad the cap didn't explode. It's not small.

 

[bhjazz]

unrelated content and link removed.

 

[bhjazz]

Replaced the caps with Rubycons (C1 C4 C5) and also replaced C6.

Still smoking. It doesn't start until the output voltage gets up over 20V.

Crap. I'll dig back through the thread and review the Regal mods although I seem to remember those were only on the amp boards, not the power supply.

Edit: Wondering if it is possible the MOSFETs are blown. I've never seen the output voltage to get past ~20V and that's when the smoking starts. (And I can't locate *exactly* where the smoke is coming from.)

 

[ericj]

Mosfets do blow, and they often blow as a dead short. If you have a component tester, you should be able to test it.

Other than that, maybe post pictures of the boards from multiple angles, perhaps something is installed wrong.

 

[SergeyPe]

After quite a number of years I've taken the half-assembled Bijou off the shelf to finally finish the build. One thing that made me curious was a well- discussed matter of providing a 40V bias to the heaters to overcome the 6922 cathode- heater limitation of 60V. We all know that the amphead's mod is not using this bias with the heaters tied to ground, leaving the cathode-heater voltage at 103V, and in all the 258 pages of this thread I haven't seen any indication that it created any problems to anyone. So I've taken a couple of 6922 and E88CC datasheets to verify the 60v limitation. To my surprise, the only place where it could be found was the old RCA datasheet. In Raytheon's document it's 135V, in Philips one it's 150V, in a couple of modern datasheets- from 120V to 200V. So it looks like leaving about 100V between the cathode and the heater is perfectly OK even by the factory specs.
By the way, for those who are using/ intend to use the R-80 transformer, it's very easy to introduce the amphead's logic even without the extra resistors. The R80 heater windings have the central taps, so you need just to remove R9, R10 and C7 from the PS and to connect the heater winding's central tap to the star ground.

 

[bhjazz]

Has it been an entire month? Sheesh.

I read, read, and re-read through various items in this thread and dug through what I could extract from the wayback machine version of the Cavalli Audio site.

I found my problem: the test load I hung off of the power supply was 100 Ohm, not the 100K Ohm that Alex specified. This means that across R7 I was pushing 625 watts. The 100K Ohm load only asks 0.625 watts across that resistor.

Since the original IRF820B MOSFET regulators are no longer made I tried the IRF820APBF which has very similar specs. Comparing the datasheets shows just a few changes and honestly, there is nothing else close anyway. I'm not sure how much heat the original 820Bs had to endure so dropping in the new ones seemed like the right thing to do. I also replaced R7 and R8 since I know they were subject to too much power. Which explained the smoke. I otherwise pulled most parts off of the board and tested them alone over the past few weeks. All of them were installed correctly and of correct values.

I am finally on to the next stage of wiring the heaters and then adding the 250VDC to the amp boards. Hopefully this will go without issue and I can button this one up and enjoy some long awaited tunes.

(PS: Yes, I *did* test this in my driveway. Heat and smoke do *not* belong in my house!)

 

[bhjazz]

My 6N6P tubes seem really dark. As in, I'm not even sure the heaters are powering up. I have checked all diodes on the board, along with every cap and resistor. I even disconnected the power wiring from the PS and checked the heater wiring. All matches Alex's original design. I also checked for continuity between pin 4 and 5 on both of the 6N6P tubes - continuity working.

Will power up again soon and double check the heater voltage on these, but the 6922 input tubes are glowing as expected on both boards.

Do I just have "low glow" heaters on these tubes?

 

[ericj]

My 6N6P tubes seem really dark. As in, I'm not even sure the heaters are powering up. I have checked all diodes on the board, along with every cap and resistor. I even disconnected the power wiring from the PS and checked the heater wiring. All matches Alex's original design. I also checked for continuity between pin 4 and 5 on both of the 6N6P tubes - continuity working.

Will power up again soon and double check the heater voltage on these, but the 6922 input tubes are glowing as expected on both boards.

Do I just have "low glow" heaters on these tubes?

Pull 'em out and measure the resistance between pins 4 and 5.

 

[bhjazz]

Both tubes measure 1.5 Ohm between pin 4 and pin 5.

 

[bhjazz]

I'm going to re-check my heater wiring again, but don't think it's a problem. Here's the heater wiring diagram from Cavalli Audio. (Thankfully I extracted this diagram years back as it is not available any more.)

Alex's design reads that the first twisted pair goes to the 6N6P tube heaters, then a second pair of twisted wire goes around the board to the 6922 heaters. My wiring is a little different but I kept the parallel nature of it intact:
One pair of twisted wires, one from each 6.3V tap of the transformer goes to the 6922.
One pair of twisted wires, one from each 6.3V tap of the transformer goes to the 6N6P, with a jumper between pins 4 and 5. The source of that wire is the same tap used for pin 5 on the 6922. The other wire from that pair goes to pin 9 of the 6N6P.

Ultimately this is the same wiring.

If I check my work by disconnecting the transformer (so that I don't get continuity through the transformer windings) I get continuity between these pins:
6922 pin 4 -> 6N6P pin 9
6922 pin 5 -> 6N6P pin 4 and pin 5

I'm fascinated with the different wiring or these two tubes. For the 6922 it seems like pin 4 and pin 5 filaments get different legs of the transformer tap to get the full 6.3V, but the 6N6P gets a single tap for both its filaments at the same time, and the screen gets it's own. Obviously these tubes work very differently. I still don't fully understand tubes.

I'll reassemble everything and check voltage on the pins.

 

[SergeyPe]

Your picture shows the wiring for ECC99's. For 6N6P it should be different:

 

[bhjazz]

Well, you bring up a good point. There were only two diagrams shown on the cavalliaudio site back in the day, and those were for 6N6P and 6N6Pi. From this thread, I had thought that most people wired the 6N6P the same as the ECC99, but pin 9 of the 6N6P goes to the screen and not the other end of the heater pins. From the multitude of datasheets for the 6N6P available online, it often looks like pin 9 goes to the screen and not to the other side of the heaters (but it does with an ECC99.)

Your diagram specifically calls out the 6N6Pi, so I went with the other diagram. (I did run across a link online which specifically reads 6N6P, 6N6PI (6H6n, 6H6nN) which makes me laugh since it suggests both tubes would be wired the same.)

I know the 6922 tubes need opposite legs of the transformer to make the full 6.3V circuit work, so I'm thinking that the jumper should be between pins 5 and 9. Or maybe not at all?

More reading and testing ahead.

Thanks, SergeyPe.

 

[bhjazz]

Also, this:
"The ECC99 is a modern tube from JJ. It's based on the 6n6p, but has higher plate resistance."

From this post:
https://www.head-fi.org/threads/bijou-all-tube-futterman-headphone-amplifier.277541/post-13232195

I am also seeing that the 6N6P does require power to the screen (pin 9) in most schematics which use that tube. I'll try to jumper pin 5 to pin 9, although I still don't believe that Alex's diagram would have been incorrect.

PS: If anyone know the true answer here for the 6N6P...I'm all ears!

 

[SergeyPe]

which makes me laugh since it suggests both tubes would be wired the same

If you check the original 6N6P and 6N6PI datasheets here, you'll see that they should be wired exactly the same way. The two heaters in 6N6P/ 6N6PI are connected in parallel inside the tube, so 6,3 Volts should go to pins 4 and 5. The screen (pin 9) has nothing to do with this circuit and shouldn't be connected at all.
Two ECC99 heaters are internally connected at pin 9, while their other ends go to pins 4 and 5. So to wire them in parallel pins 4 and 5 should be connected together with 6,3 Volts applied between pin 9 and pins 4+5. This is exactly what is shown on the diagrams.

I know the 6922 tubes need opposite legs of the transformer to make the full 6.3V circuit work

What do you mean by the opposite legs? All the heaters for all of the tubes are connected in parallel to one 6,3 Volts heater winding of the transformer.

 

[funch]

I built a Bijou back when it was first revealed. Sergey is correct. Wire the heaters following the original diagram in his post #4,271 and be done with it.

Only wire to pin 9 when using the ECC99 tube.