[L0rdGwyn]

I think it's technically the "Fitz mod" to address the hum, but close enough.

And I actually have all the necessary parts in stock. Well, the 10uF cap I have is 450v, but close enough (and it's only slightly bigger)...

Let us know how it goes

 

[Paladin79]

My Darkvoice just arrived, luckily I saw an UPS email. It was placed in a plastic bag and dropped into the snow near my driveway lol.
Most likely I will work on an extension for @bcowen then get back to my changes after I work on a more pressing project. I will show the outside of my finished amp when my changes are complete.

 

[Deceneu808]

So my 5998 tubes started doing funky crap again. One of them has almost no sound in the right channel and a little distortion. The second one plays almost full volume but distort like hell. Should I try to add solder on the pins ? They look as if they have nothing left there. I'll try to snap a few pics but I doubt it will show on the photo. Any other suggestions ?

 

[Mr Trev]

Speaking of future designs...


This got the gears turning though, could be interesting to load the cathode follower with a low turns ratio output transformer, maybe 2:1 or 4:1 to lower the output impedance further, although they would be large to handle 100mA without saturating, also wouldn't be an OTL anymore I might explore this idea.

Would it be possible to have it both ways? Dedicated hi/lo impedance outputs?

 

[Paladin79]

So my 5998 tubes started doing funky crap again. One of them has almost no sound in the right channel and a little distortion. The second one plays almost full volume but distort like hell. Should I try to add solder on the pins ? They look as if they have nothing left there. I'll try to snap a few pics but I doubt it will show on the photo. Any other suggestions ?

If you try re-flowing or re-soldering the pins and it does not help, I should be around this evening and I will talk you through more detailed solder replacement.

 

[Deceneu808]

If you try re-flowing or re-soldering the pins and it does not help, I should be around this evening and I will talk you through more detailed solder replacement.

I wrote back in a post, the tubes worked fine for about an hour until this. I reflowed the solder on the pins meaning that I used a heated hammer for about 10-15 seconds and then I've spread it around the tip of the pin. Did this. Both tubes worked fine. Only tested them a track or two and left one in the DV and another went in to the box of tubes. Now a few days later the one in the DV started to distort again. For a second I thought it was my headphones. I'm on my second pair of DT880 so my first thought was "not again..." But I switched the power tube and they work fine. I did the whole process again of reflowing but this time with no success. They won't work.

 

[L0rdGwyn]

Would it be possible to have it both ways? Dedicated hi/lo impedance outputs?

You sure could, just use a transformer with multiple output taps. I've put together some simulations of this idea, it will work, just need to find a happy medium between the gain of the input tube and the turns ratio of the output transformer. Note that with a cathode follower output operating at unity gain, the entire voltage gain of the amplifier is generated by the input stage, so you don't want to be in a situation where the input tube has to swing large amounts of voltage and distorting to generate a reasonable output on the transformer secondary. Restated, the cathode follower provides no voltage gain and the transformer steps down any voltage gain generated by the input tube, so a reasonably low turns ratio OPT is likely the way to go. Will also need a cathode resistor between the OPT primary and ground to bias the cathode follower, so there will be a slight loss of output voltage there as well.

 

[bcowen]

I wrote back in a post, the tubes worked fine for about an hour until this. I reflowed the solder on the pins meaning that I used a heated hammer for about 10-15 seconds and then I've spread it around the tip of the pin. Did this. Both tubes worked fine. Only tested them a track or two and left one in the DV and another went in to the box of tubes. Now a few days later the one in the DV started to distort again. For a second I thought it was my headphones. I'm on my second pair of DT880 so my first thought was "not again..." But I switched the power tube and they work fine. I did the whole process again of reflowing but this time with no success. They won't work.

Definitely sounds like a solder problem. I've had a total of 5 Tung-Sol / Chatham tubes that have had pin solder issues. None of them 5998's, but 6AS7's and 6080's. On a couple of them when I sucked the solder out there was almost no solder in some of the pins at all. We know at this point that the older Russian tubes (Fotons and Melz anyway) have a high incident rate of pin solder issues, but my experience with the Tung Sols / Chathams is that the incident rate is nearly as high. Best to do a thorough sucking job and then replace with a decent amount of quality new solder, especially for tubes as expensive and desirable as a 5998. If you don't have a "sucker," the Soldapullt that @Paladin79 mentioned a while back isn't expensive and works very nicely.

https://www.amazon.com/EDSYN-The-Or...d=1&keywords=soldapullt&qid=1613584134&sr=8-1

 

[bcowen]

Let us know how it goes

Will do. I will probably do this mod first before I mess with the output caps and make sure nothing blows up before I put in $100 worth of Mundorfs. Plus I need to order another pair of the 47uf ones anyway....

 

[Deceneu808]

Definitely sounds like a solder problem. I've had a total of 5 Tung-Sol / Chatham tubes that have had pin solder issues. None of them 5998's, but 6AS7's and 6080's. On a couple of them when I sucked the solder out there was almost no solder in some of the pins at all. We know at this point that the older Russian tubes (Fotons and Melz anyway) have a high incident rate of pin solder issues, but my experience with the Tung Sols / Chathams is that the incident rate is nearly as high. Best to do a thorough sucking job and then replace with a decent amount of quality new solder, especially for tubes as expensive and desirable as a 5998. If you don't have a "sucker," the Soldapullt that @Paladin79 mentioned a while back isn't expensive and works very nicely.

https://www.amazon.com/EDSYN-The-Or...d=1&keywords=soldapullt&qid=1613584134&sr=8-1

I will be buying everything from my local hardware store. What else do I need besides the "sucker" ? You guys will have to walk me through

Will this work ?

or this

 

[bcowen]

I will be buying everything from my local hardware store. What else do I need besides the "sucker" ? You guys will have to walk me through

You'll need some good quality solder (if you don't have any), and a small metal file will help smooth off the edges at the tip of the pins when you're done. And quite honestly, the Soldapullt is the only plunger-type sucker I've used that works. I've tried probably a half-dozen different ones over the years and frankly they all sucked....or didn't suck, in this case.

https://www.amazon.com/gp/product/B004DEUYBY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[Paladin79]

I use liquid rosin to help cleanse the inside of the pins, rosin flux. Never use acid flux in electronics unless you are trying for tiny little batteries.

 

[Deceneu808]

You'll need some good quality solder (if you don't have any), and a small metal file will help smooth off the edges at the tip of the pins when you're done. And quite honestly, the Soldapullt is the only plunger-type sucker I've used that works. I've tried probably a half-dozen different ones over the years and frankly they all sucked....or didn't suck, in this case.

https://www.amazon.com/gp/product/B004DEUYBY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I will not be able to find exactly those in my area but I'll do my best to pick up the highest quality pump I can find and solder.
But how does the process work exactly ? Do I need to heat and quickly suck with the pump ?

 

[Paladin79]

I will not be able to find exactly those in my area but I'll do my best to pick up the highest quality pump I can find and solder.
But how does the process work exactly ? Do I need to heat and quickly suck with the pump ?

Yes

 

[Deceneu808]

Yes

I will extract all the "old" solder that's on there until I see inside of the pin right ? I can see that some pins even on some other tubes have a little hole opening on the tip the pins.
And then apply a new solder ?