sex 2.1 right side is hot

[dtroise@bellsouth.net]

Hi all
This is my first post, I just fired up my sex 2.1 with impedance sw and cs 4 upgrade, all the voltages checked fine, the heater voltage is a little low 2.76 volts on all terminals, after running it for about an hour I checked the heat with a greenlee temp gun.( It is very accurate), what concerns me is that all items on the top right side run about 50 degrees hotter than the left. Ex: right choke, 151 f  left choke 94, right tube 294 f, left tube 245 f , TX 134 f.  I swapped the tubes and the difference stayed the same
I re soldered all of the connections on the right side and left as well, any suggestions would be appreciated                  Thanks Don

 

[Doc B]

Infrared thermometer? They are pretty difficult to get consistent readings with, and there is usually a pretty severe temperature gradient across things like tubes. Slight changes in the targeting dot position can often make big differences in the reading. I drove myself crazy trying to read the heat sinks consistently on the Stereomour regulated DC supply board when we were working on the design. Air flow around the amp can have an effect on the temp of the different components too. If the voltages are correct everywhere both sides are dissipating the same power. If you have the feet on the bottom of the base everything is probably OK.

 

[dtroise@bellsouth.net]

Thanks for the answer, however the temp gun is accurate and I make sure that the dot is in the same spot and distance on the components I used this gun at many electrical installations to find loose connections. I installed better feet. The tube I understand but the choke is what concerns me, you cannot hold your finger on the hot side but no problem on the cold side.
What should the normal operating temp be? The top plate is 120 f all around and a  hotter by 10 f on some of spots near the tube and choke, The Tx runs 130 on all corners. I have multiple tube gear and the ones that have chokes do not run past 90 F just like the left side.

 

[Doc B]

The S.E.X. was designed to be as compact as possible. The iron is thus made as compact as possible, sits in close proximity to the tubes and to other inductors. Subsequently it is designed to run at pretty high temperatures and the parts do get quite hot to the touch. If the temperature imbalance is coming from the plate chokes, the simple way to determine whether the cause is internal to them is to measure the DCR of each choke and measure the voltage drop across each one. From that you can calculate the power dissipated, V^2/R. If the power is about the same for each plate choke that would not be the cause of any thermal imbalance. Ditto for any other components that dissipate heat like cathode resistors.

I should probably mention that a plate loading choke typically has quite a bit higher inductance than the filter chokes on most tube amps, and the DCR will be higher than the typical filter choke because of the greater number of turns of wire needed to achieve that. Higher DCR and higher voltage drop means more heat is dissipated.

Naturally I can't be sure of what better feet means in terms of airflow, but I'll presume that they raise the base off whatever it is sitting on at least as high as the stock feet do. If not, they will need to be a little taller.

Another possibility that could create some imbalance is if the chokes have not been mounted with the hardware in the same order. That is to say if the fiber shoulder washers are not under one choke it could run at a different temp than the one that is on the shoulder washers. Not saying that this is the case, just trying to offer some possible scenarios.

The bottom line is that we are primarily concerned about the operating voltages and currents, which correlate with the sonic attributes of the amp. Double checking those parameters is the best way to assure that the temperature differences don't indicate a problem in the components or construction.

 

[dtroise@bellsouth.net]

Hi Doc
In answer to your question better means bigger and higher for the feet, yes the fibre washers were installed. All hardware exactly to spec.
I have run measurements for voltage and r which differ from my first run when it was fired up the first time, I believe that I did not let it settle in long enough at that time. this time I left it to warm up for two hours, I have found that the A side which is the hot side has a lower voltage across all parameters and at the choke #6 and A2 the voltage fluctuates in a 9 to 14 volt range. The voltage is considerably lower than spec coming off the t 4 & t 5 I am not sure but it appears to me that the problem starts at #6 I re soldered that connection twice, I must admit that it was very hard to get it to fit properly. The log is below and I would appreciate your comments before I start to take things apart.

A side choke DCR = 841 ohm B side DCR = 847

Voltage
T 1 =210    T 4 =395    T 5 = 198
T 6 = 367-380 does not hold steady T 16 =372
T 10=363    T 20 =395
T 11 =340    T 21=344
T 15= 23.5  T 25= 17.7
A-2 340 fluctuates 338-340 never holds steady B 2 353
A 3  21.5      B 3  17.5
A 5  79.3      B 5  72.4
A 6  2.3        B 6  2.3
A 7  3.39      B7    3.37
A 8  2.42      B8    2.418
C 1  3.14      C 2  3.14              All 0 volts were 0

Thanks for your help Don
           

 

[Doc B]

OK, that does indicate a different current flow from side to side on the output stage. Best place to start is something that doesn't involve any desoldering -  to swap tubes from side to side and see if the A2/B2 and A3/B3 voltages follow the tubes.

 

[dtroise@bellsouth.net]

I should have told you that I already did that and the Voltage stays the same

 

[Doc B]

OK, my understanding is that you have also been working with Josh regarding a lack of output on the right channel, which corresponds with the A tube. The A side voltages are off a bit, but not drastically, so I don't think you have a hard short anywhere. That's the good news. The bad news is the issue might be a little more difficult to find because it is showing up as only a relatively small deviation in the voltages.

Here's a few things to check -

If a capacitor gets nicked by a hot soldering iron that can create the kind of issue we are talking about. Check to see if maybe the black Solen film capacitor by the A socket has a small melted spot from an errant strike by the iron. This is easy to happen, I have done it myself a few times.

If that is OK, make sure the orientation of the striped side of the 1000uF 35V cap and the 22uF 450V cap at the A socket are both oriented with the striped side lead on the proper terminal. If these are reversed they can break down and draw extra current. While you are at it verify the 100uF 450V cap is oriented correctly too.

 

[dtroise@bellsouth.net]

Hi
The problem with the headphone jack is mechanical, the top right terminal does make contact with the plug in or out I can get it to work by prying and bending but it does not stay functional.

I did nick the solen cap on the A side but it looks like only paint came off, if I change them can I use a 1 uf as I have that in an ampohm paper and wax 630 v and a sprague orange drop 400 v  but I am not sure if the heat is a factor for these caps

All caps are oriented properly,

Don

 

[Doc B]

Maybe post a pic of the Solen. Don't want to make you pull it out unless it looks bad enough to be a problem.

 

[dtroise@bellsouth.net]

Hi Doc
After a closer inspection it appeared that I did damage the solen cap. I cut it out and clipped in a cap from my cap bank that I keep on hand  however they are all 1 uf. The voltage is perfect now on both sides, steady and equal, I have enclosed a pic of it, before I solder these in I would like to know your opinion on 1 uf
Thanks for your help you hit the nail right on the head.

Don

 

[dtroise@bellsouth.net]

I forgot the attachment

 

[Paul Joppa]

A parafeed cap of 1.0uF should work well in the SEX 2.1.

My calculated nominal capacitance would be 1.25uF, so 1uF is as close to the calculation as is 1.5uF. I generally say "half to twice the calculated value is an acceptable range." You may hear a difference between 1.0 vs. 1.5uF, but it won't be large. You are unlikely to prefer one over the other even if you do hear a difference.

The technical tradeoff is between bass extension and bass power handling. More significant (IMHO) is the variation between different speakers (and room acoustics). That variation invites experimentation with the capacitor value if you want to optimize for your speakers, your room, and your personal preferences.

 

[dtroise@bellsouth.net]

Thanks for that info

Donald Troise

 

[dtroise@bellsouth.net]

The amp is up and running, the voltage is to spec and equal on the A&B sides the heat has disappeared, I can hold my hand on any part as it is only warm to the touch. The headphone jack works perfectly, I have not tried speakers as of yet because I can't stop listening to this magical amp.

The damaged capacitor did cause three other problems which I found and repaired with the excellent documentation that is supplied. I am losing my concentration writing this because the magic of this amp keeps sucking me deeper into audio nirvana. I am listing the other problems that I caused by nicking the 1.5 solen cap with my iron.

The volume pot lost its right channel with the voltage instability, I changed it to a 21 step attentuator  BTW I was going to do that anyway,
The signal voltage started to show 59 v at the cap, The 35 v 1000uf cap was starting to bulge I changed that to a dale 40 v 1000 uf and checked the 249 k r and found that to be blown, I could not see any physical damage as it had blown apart on the bottom, I made up two resistors in series to be 249 k, ( I will change when I get the new one) . That was all the damage I caused by just nicking the solen cap.
While I was at it I installed a pseudo center tap for the heater voltage, I am listening with audeze lcd 2 fazor headphones .With no music playing and the volume control to max I have to press the cup hard to my ear to hear the slightest bit of hash, I have the imp. sw. set at 32 ohms, I have not tried any other settings because I can not turn this amp off, it is a pity that it was retired I feel like one of the lucky ones .

That' it for now

Thanks to Doc and the team for this wonderful amp

Donald Troise

 

[Doc B]

Thanks for the kind words! Glad it's all sorted out.

 

[Natural Sound]

I have not tried any other settings because I can not turn this amp off, it is a pity that it was retired I feel like one of the lucky ones.

My first experience with Bottlehead was a S.E.X. 2.0 amp That I built back in 2005. It has Magnequest Iron, cap upgrades and C4S. I still use that amp pretty much daily. I also bought a S.E.X. 2.1 during one of Bottlehead's sales. I still need to put the finishing touches on that one. Additionally I bought two more un-built units from Jim R. So all totaled I have 4 of them. Two 2.0's and two 2.1's. One of them is on permanent loan to a friend. The S.E.X. amp continues to be a favorite of mine. I plan on keeping mine going as long as I can. Its truly a special little amp.

 

[dtroise@bellsouth.net]

I could not agree more.

I have a multi amp system through a Rane brown face active c/o with linkwietz Riley slope, a total of 6 amps, all tubes, Mc Intosh MC 40' Dynaco st 70, Dynaco M40, Shannon Parks design Go Set Go, directly heated triode

I have rebuilt all of them, both Dynacos now have a Mullard Pentode long tail phase splitter front end designed by Dr Lloyd Peppard, point to point. ( no pcb) the EL 84 tubes are wired into triode. The Go Set Go is a wonderful directly heated SET , when I built it I upgraded the caps,to Russian teflon I am not sure that I like them.In the Dynaco' I used Mundorf film, and sprague atoms the Mcs I left stock, I did not even change them to a star ground.

I have listened to each through headphones and I can honestly say that the SEX 2.1 is the most magical sounding of the group. Of course this is a two edge sword as I am going to use it for my Audeze lcd 2.1 and Fostek folded horns serving the front channel surround of the Home Theater.

I have been contemplating listening to my vinyl playback through it but I am afraid that it will never make it back to the Home Theater and then what would I do with all of those speakers and amps in the critical listening room.

 

[Doc B]

Shannon lives not too far from me. Very nice guy.

 

[dtroise@bellsouth.net]

I think that Pete Riggle is not far from you either, I have a custom Woody Tone Arm from him, it is glorious