[baronbeehive]

I noticed an issue with my amp, that sometimes the left channel would not work or play loud static unless the preamp tube was cocked a little bit to the right. It was also more microphonic than I remembered, no matter what tubes I used. I discovered the #8 pin socket needed retensioning, and now the static and weird microphony are gone............

Did you do a continuity check from the newly soldered cap leg on the left channel to the trace and wiggle the leg to see if there is a break in the circuit? If so the soldering needs fixing. The board is quite flexible, not very rigid, and any movement in the socket could affect other points on the board. Also you could find out what each pin is connected to on the right channel socket and check the continuity of the left had socket to see if the contacts are the same on that side, if it is the socket then there will be a poor connection on one of the pins indicated by a break in continuity.

Edit: I don't really see a problem with the amp or its components, surface mount components should not fail, and the amp doesn't get hot so overheating is not a problem, so the mechanical force of changing tubes on the sockets is the most likely cause of failure I would have thought.

 

[Makiah S]

I noticed an issue with my amp, that sometimes the left channel would not work or play loud static unless the preamp tube was cocked a little bit to the right. It was also more microphonic than I remembered, no matter what tubes I used. I discovered the #8 pin socket needed retensioning, and now the static and weird microphony are gone. I also changed the cathode bypass caps again, this time from Elna Silmic 220uf 25v to Wurth WCAP-PT5H 1000uf 6.3V aluminum polymer caps. The top end came back and clarity is also better, without killing the bass boost the 0.47uf coupling caps provide.



Can you post a link to the adapter you bought? Even with the 9-pin socket being recessed, I don't have a problem using this adapter as-is:

http://www.ebay.com/itm/1pc-12SN7-1...948306?hash=item2ec9315212:g:BZgAAOSwwbdWLixO

The one I got is much wider than the one you've posted. I guess I'll just get both and see if there's a difference sonic ally [I doub't there will be but I always like to have doubles of everything anyways]

 

[Miguel Dominguez]

I tried the cap upgrade for this amp and got myself into bit of a bind...

Long story short... four gold washers fell out of the bottom of the amp while I was removing screws. I was unable to find the correct places for them (the bottom plate would not sit flush) so I left them out and then reassembled. I blew the fuse when trying to power it back up. Any idea where these washers go and if they would somehow cause a short if not installed? I'm pretty confident that the caps were installed correctly as I've built a few bottlehead kits. Any help would be appreciated!!

 

[Maxx134]

Pics would help, and I myself don't remember any washers...
Also, if you extended the bottom you have to be careful that overtightening the screws will bend the board.

 

[Miguel Dominguez]

Ok, figured it out. The 4 gold washers belong between the metal plate on the top side and the pcb. This keeps the metal plate from shorting out the circuit... One would not normally need to remove this metal plate to do the cap mod, it turns out. I fixed that, but wound up blowing another fuse. There is a short somewhere... I'll post some pics in a few.

EDIT:

Pics: https://imgur.com/a/dt2Xt

 

[baronbeehive]

Ok, figured it out. The 4 gold washers belong between the metal plate on the top side and the pcb. This keeps the metal plate from shorting out the circuit... One would not normally need to remove this metal plate to do the cap mod, it turns out. I fixed that, but wound up blowing another fuse. There is a short somewhere... I'll post some pics in a few.

EDIT:

Pics: https://imgur.com/a/dt2Xt

Maxx, he could just check one of two things before you come back....

Check:
1 - the ends of the cap legs between R24 and R26, are they touching the top plate when reassembled, if so trim off the ends.
2 - the wires to the transformers have not broken off
3 - I don't know why the bottom plate is not flush, find out why.

One of the reasons it's quite an easy amp to mod is all the components are easily accessible on the board and it's fairly clear by looking if anything does not look right, for example poor soldering joints or bits of solder left lying around.

Edit: Have you got a pic of the bottom showing your new caps?

 

[Miguel Dominguez]

Maxx, he could just check one of two things before you come back....

Check:
1 - the ends of the cap legs between R24 and R26, are they touching the top plate when reassembled, if so trim off the ends.
2 - the wires to the transformers have not broken off
3 - I don't know why the bottom plate is not flush, find out why.

One of the reasons it's quite an easy amp to mod is all the components are easily accessible on the board and it's fairly clear by looking if anything does not look right, for example poor soldering joints or bits of solder left lying around.

Edit: Have you got a pic of the bottom showing your new caps?

Yep. See the imgur gallery in post #486. The cap leads are a bit long. I'll go ahead and snip them a bit more, but there seems to be ample space between the top plate and the board once it's screwed on. Not sure if the leads are long enough to have caused a short. The metal plate (the one that covers half the board when viewed from the top) shorting out the entire circuit makes sense since I did not reinstall the washers/risers after turning on the amp after the mod. My question would be... could the amp be dead? Would the blown fuse have prevented any critical damage to the components?

 

[baronbeehive]

You may be alright, also there may be a safety cut out but I don't know if there is on this amp.

I would do a continuity check first on the new components you fitted to eliminate this, then also find out the most likely thing the metal plate may have shorted underneath it and go from there. I haven't seen any pics of the topside so can't tell what it might be. I'm a bit surprised that washers would have made much difference to the height of the plate though, I think most likely your mods!

Do you have a multimeter? As you may know I had to rectify a couple of problems on the amp after modding but I checked continuity before I switched everything back on again because I knew that there were 2 suspect connections.

I can't see a pic of the new caps unless this is it:

Oh sorry I see this is it, it looked like the original caps before the pic was blown up! It all looks fine, the only way you will find out is by testing the circuit as I said unless Maxx can help.

 

[DavidK35]

Gemtunes Amp part 3

Thanks to Mr Slim for repairing & modifying amp with the Auricap capacitors, he does excellent work.
I have to agree with everyone here the change of caps definitely add to the bass without any detriment.
Difference is not night & day but noticable & well worth doing, very happy with this amp.

First I went back to the 12SL7 drivers & gave them another 24 hrs burn in on top of the 3 days they
already received and no change. Do not know what others see in this tube, but for me this came a very long
last in choice of driver. All other testing was done with 6211/14F7/14AF7/14N7.
4 of these drivers were very very close in performance, the only one that I did not like too much was the 14F7
which I found to be a bit too much in your face & a hair coarser. The other 4 were much closer with the loctals having a very slight edge on the 6211, but would be hard to pick in say a blind test.
I am not going to go into great technical detail but just list my order of preference based on the listening impact
each had.
1) 14AF7
2) 14N7
3) 6211A (GE 5 star black plate, double mica)
4) 6211A (RCA black plate, triple mica)
5) 14F7
Wow the much cheaper GE 5 star slightly outdid the fancy RCA tube. Very suprised.
Unfortunately the 14AF7 died on me after a short time & had no spare. Have ordered more and will retest some
more because it was not long enough of a test. But really any one of those would be fine & dirt cheap too.
Although the branding can vary, as I understand it these loctals are all made by Sylvania.

Power tubes test with above drivers in order of lowest to highest (opposite to above).

6V6GT Weak bass & over emphasized treble. Not my cup of tea at all.
6K6G Very smooth good for long listening session, a touch less detail.
6F6GT Great tube, good in all departments, good soundstage, forward presence
6BG6GA Same as 6F6 but more soundstage. "surround" sound comes to mind, more enveloping.
6BG6G As above but seemed like the singer was right in front of me up close & personal, nose to nose, LOL.

Really all except the 6V6 were all enjoyable listening experiences, differences were not great but
I do think the 6BG6's are something special, certainly the best tubes I have come across. It is well worth the small
extra cost for the adaptors to experience the best (IMO) this amp has to offer. Unfortunately something I did not take into account is the G coke tube is even taller than the tall straight tube, so there is a real problem with the adaptors that had to be stretched (external wire) really tight (not good or recommended) so I cut that test short & ordered a new set of custom adaptors with longer wires (same price).
IMO the straight tubes look pretty cool but they do not have to have risers like mine (adds another 11/4"), but the coke ones look a bit on the ridiculous side, however I am just looking for the best sound so I dont care about that.

The conclusion will be when I get the new 6BG6G adaptors & 14AF7's for more listening tests, but at the moment this is my personal best combination.

 

[baronbeehive]

Gemtunes Amp part 3
.....

First I went back to the 12SL7 drivers & gave them another 24 hrs burn in on top of the 3 days they
already received and no change. Do not know what others see in this tube, but for me this came a very long
last in choice of driver. All other testing was done with 6211/14F7/14AF7/14N7.
4 of these drivers were very very close in performance, the only one that I did not like too much was the 14F7
which I found to be a bit too much in your face & a hair coarser. The other 4 were much closer with the loctals having a very slight edge on the 6211, but would be hard to pick in say a blind test.
I am not going to go into great technical detail but just list my order of preference based on the listening impact
each had.
1) 14AF7
2) 14N7
3) 6211A (GE 5 star black plate, double mica)
4) 6211A (RCA black plate, triple mica)
5) 14F7
Wow the much cheaper GE 5 star slightly outdid the fancy RCA tube. Very suprised.
Unfortunately the 14AF7 died on me after a short time & had no spare. Have ordered more and will retest some
more because it was not long enough of a test. But really any one of those would be fine & dirt cheap too.
Although the branding can vary, as I understand it these loctals are all made by Sylvania.
.....

I see from your previous post that you list the 12SL7's you tried as Westinghouse and RCA, did you try the Tungsol 12SL7? My only criticism of the 12SL7's is the opposite to your experience, I find them a little too soft if anything, apart from that they sound fantastic, but I keep going back to my 5751's though. I'm waiting for some silver plate GE12SL7's to see if the treble is anymore exciting sounding to see if I agree with what others have said, I think as I have more bass in my speaker APPJ that enhanced treble might sound good, but frankly I am very happy with the set up as it is.

I haven't come across the others you list at all so all very interesting.

 

[DavidK35]

I see from your previous post that you list the 12SL7's you tried as Westinghouse and RCA, did you try the Tungsol 12SL7? My only criticism of the 12SL7's is the opposite to your experience, I find them a little too soft if anything, apart from that they sound fantastic, but I keep going back to my 5751's though. I'm waiting for some silver plate GE12SL7's to see if the treble is anymore exciting sounding to see if I agree with what others have said, I think as I have more bass in my speaker APPJ that enhanced treble might sound good, but frankly I am very happy with the set up as it is.

I haven't come across the others you list at all so all very interesting.

Well I wonder then that since you have a different amp to the rest of us, that might be the reason the 12SL's work better for you?.
Previous experience with other amps I have found the 7/14 loctals perform better than the 6/12SL's. All the 14's have metal bases
so do not know if this is a factor. Mostly I have read that the metal based 6SL/N7 tubes are highly sought after.14/7 adaptors are inexpensive & the tubes will only set you back $7 or $8 a piece.
Just burning in my nos 14AF7 atm & waiting on the new adaptors for the 6BG6G's. The 6211 (12AT7 type) IMO is a totally underated/ignored tube
and deserves more respect (you can get GE 5 star 6211A's for $3 a piece). I did extensive tests over a long period of time in the past & these tubes outperformed all other 12AT7 types.
Of course we all like different types of sound but this one stood out for me personally.

 

[Maxx134]

I do think the 6BG6's are something special, certainly the best tubes I have come across. It is well worth the small

I have these and waiting for the adapters to try.

I also found some 6Q5G tubes and wondering if anybody knows or tried them.
I will make sure the pinout is ok to put them in and try them over weekend.

The 14AF7 will also take a while for my adapter to come in from china so its a waiting game but am already happy with my selection.

My question would be... could the amp be dead? Would the blown fuse have prevented any critical damage to the components?

Try using different tubes, otherwise unknown how the PSU handled your shorting as this unit has some tiny surface mount parts that may have been damaged.
Try with new fuse first and leave open to make any note of anything getting hot or abnormal.
You will need tester to measure voltage as well for repairs, but for now just observe and try not to touch anything and try turn on unit upside down so you can see bottom.

Good luck

 

[Maxx134]

I updated my post to check that broken amp

 

[Maxx134]

Thanks to Mr Slim for repairing & modifying amp with the Auricap capacitors

So you only upgraded the coupling caps?

More gains to be had with upgrade of the cathode caps.

 

[DavidK35]

So you only upgraded the coupling caps?

More gains to be had with upgrade of the cathode caps.

Yes that's right, after reading the whole thread I decided that the changes indicated from the other mod were not for me.

If you have ordered adaptors for the 6BG6 "G"s then I hope you have ordered them with longer external wires than normal.
The ones I got initially were only suitable for 6BG6 "GA"s. The ones I have on order now are 20mm longer.

p.s. if your 14AF7's are NOS I recommend at least 3 days burn in, they take a while.