Need help with an unusual problem

[Paul Joppa]

This is a real puzzler, all right.

At least we've found a symptom that explains the one-sided clipping problem. The 6922 bias is too low and it is going into grid current, clipping one side of the waveform. The problem is, the voltages and currents don't make sense

The only idea I have left is a possible radio-frequency oscillation problem. Those are usually dependent on layout and lead dress, so any non-standard component or change in wire routing becomes a suspect. Can you locate the original 100uF caps and install them on the PC board as shown on page 70 of the manual? Leave the film caps detached from the cathodes. Are there any other deviations from the stock configuration? They may have to go, too.

 

[Larpy]

I don't seem to have any 100uF electrolytic caps in my cap drawer.  I'll order a couple from Mouser.  If I remember right, they were Lelons?  This is probably a question for Doc: have Eros kits been shipping with Lelon 100uF/160v caps recently?  I'll play it safe and order a pair of Lelons and a pair of Nichicon UCY caps--they're rated for 12,000 hours.

I'll report back once the caps have arrived and I install them.

Here is the complete list of the other non-stock components in the Eros:
• SBE 716P "orange drop" caps in the RIAA network
• Auricap caps as the output caps
• 0.1uF Russian K40Y-9 caps on the voltage regulator board
• Dale CPF 2 watt 47K Ω plate resistors for the 6922 tube
• Vampire RCA input jacks

The big Panasonic caps are the only component that required non-stock lead dress.

The interesting thing is that most of these components were imported from my first Eros.  I used the Panasonic, Auricap, and Russian caps in my first Eros for a year and a half with no problem.  Quick recap:  I happily used an Eros for a year and a half when, last fall, it suddenly started sounding distorted.  My attempt to identify the problem turned into a nearly comical creation of new problems, but I'm 99% sure the original problem was a flaky transistor solder connection.  But I got so frustrated I ordered a new Eros kit during last Thanksgiving's BH sale.  I put this new kit together with all new parts except for the Panasonic and Auricap caps--they came off my old Eros and were installed in my new Eros.

I gave my first Eros to an audio friend, but he's out of the country until later this month.  Otherwise, I'd have him come over with my old Eros to compare.

 

[Larpy]

100uF caps arrived today and I soldered them in to the board above the 6922 tube socket as shown in the instructions.  I put the Bugle Boy 7308 tube back in (it seems the happiest of the ones I have for duty in that socket) and the measurements looked better:

pin 1:  167v        pin 6:  161v
pin 2:  94v          pin 7:  95v
pin 3:  96v          pin 8: 97v
pin 2 to 3:  1.6v  pin 7 to 8: 1.3v

I hooked the Eros back into my system but unfortunately the distortion is still there.  And the asymmetrical waveforms.

I guess the next step is to remove all the other non-stock components I've used.  Since I was ordering the 100uF electrolytics, I also ordered replacement Dale resistors that get soldered to pins on sockets A-C (the same ones that came with the kit).  I think I'll rebuild all three sockets and their connections and go really, really slowly.

 

[Paul Joppa]

I don't have a better suggestion at this point. I wish I did!