2A3 SET Amp. I'm despondent ! Please help/advise.

Discussion in 'Tube Audio' started by SixCats!, Jan 11, 2019 at 8:52 PM.

  1. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi all,

    In a Nutshell (for reasons unknown) my (new to me) 2A3 SET Mono Amp (I'm thinking) is the cause of
    a sudden decrease of volume on my Tru-Sonic Horn. At first, I thought the problem might be the Tru-Sonic Horn itself as I had earlier this afternoon taken the back off (VERY carefully) as I had planned to change out the Bass driver until I realized it was NOT going to be such an easy exchange so, I abandoned that plan. While I had the back cover half off, I did take the opportunity to De-Oxit the Horn's two L-Pads. After that, I carefully replaced and buttoned up the back cover. Several hours later, I turned on my SET Amp and right away noticed that the Volume was perhaps 25% of what I had experienced last night. So, as a test, I played the same (good recording) CD disk that I first ever played on this System last week (which sounded GREAT) however tonight, I'm experienced a great loss of volume. My first thought was, I screwed up something (wiring ?) to the Horn Speaker by removing the back cover (tight wiring). So, I disconnected the SET Amp from the Horn and connected my Mono Pilot PT-1030D (EL 84) Amp and, the Horn plays/sounds fine (and LOUD). Of course the Pilot Amp is 13 Watts or so (vs. the SET 2A3's three Watts). That being said, the other night, the 2A3 played equally as loud with ease. So, I again reconnected the SET Amp back up and tried different interconnects (direct from CD Player into Amp) as well as two different CD Players. Ugggh, still a "no go" for the SET 2A3 and volume. Guys, I'm not sure what to think as I'm very new to the SET Amp World. Is it possible one (or more) of the SET Tubes suddenly became weak to such an extent that it can cause such a noticeable difference/loss in volume ? I mean a night and day difference. I VERY much would appreciate any help/suggestions/recommendations on what I should do about this situation. I already miss my 2A3 SET.
    Thank you in advance for any help you may offer.

    SixCats! in Maine (singing the Blues)
     
    Last edited: Jan 11, 2019 at 9:15 PM

     

    Please register to disable this ad.

  2. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    53,130
    Don't panic!
    You have made lots of incremental changes -- and now you have an unwanted change correlated with it*.

    Check your wiring, all of it. Did you knock something loose, get some strands touching each other, etc?

    EDIT: I do mean all your wiring -- cable from your source (record player?) to the amp, and connections at the amp, too. I've had all sorts of weird thing happen with turntable connections/connectors ('specially older ones) when I went futzing around with a hifi system).

    My guess (FWIW) is there are bad spots in your L-pads; try 'fiddling' with them (the technical term) a wee bit, and see if you can get them, even instanteously, to sound louder.

    ____________________
    * Remember, though, that correlation isn't causation :)

    [​IMG]
     
    Last edited: Jan 11, 2019 at 9:10 PM
  3. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Mark,

    Ugggh. I'm trying NOT to panic! I earlier did "fiddle" with the L-Pads. I've only noticed a change in tone (Tweet Horn) and (Bass Driver) as opposed to Volume change. I will check (again) all wiring/connectors. I would sure hate to have to get back into that Horn Cab but, if all else fails, I'll have to check to make sure nothing (wiring) came loose. That being said, the Horn seems to sound fine with the Pilot Amp. I just De-oxit the four Tube sockets. Perhaps this will help however, I will not attempt to "Power up" the SET Amp again tonight. I will check all wiring (again). Thanks Mark for your help.

    SixCats! (aka Tom) in Maine
     
  4. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Mark,

    I think you are correct. That is to say, I now believe there is "something" wrong with the Tru-Sonic's L-Pad(s). I hear/detect NO change whatsoever in one of the L-Pads when turning knob.

    Man, I hate to think that I somehow messed it up today by spraying De-Oxit into the Pads. Then again, perhaps being a (plus) sixty year old Speaker, the L-Pad is just worn out.

    I just now connected the SET 2A3 to my Brociner Back Loaded Corner Horn (single 12" University 6201 Coaxial) and the volume is MUCH louder now than the Stephens Tru-Sonic

    (which was NOT the case the other day). I will continue trying to figure this situation out but, my "Gut" feeling is now that the Tru-Sonic has a volume "issue" due to the L-Pad(s) especially

    when using the 2A3 SET whereas the Pilot EL 84 appeared to "power through" and provide very good volume. Ummmm........

    SixCats!
     
  5. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    The next morning......(Saturday Jan. 12th. 2019)

    Ummmm......perhaps "Ghost in the Machine" ? Today, the Tru-Sonic Horn is playing louder than last night when I was in my Panic mode. However, not as loud as it did when I originally first played with the 2A3 SET last week when first purchased. As mentioned above, last night, I pulled all four Tubes and De-Oxit all the Sockets, input, Controls,etc. I also cleaned the Tube's pins and (several times) removed and reinserted the tubes into their sockets. I still can't help but wonder if I may have "tweaked" something while undoing the Horn's back cover and/or perhaps my spraying De-Oxit into the L-Pads had a "temporary" ill effect ? That being said, I'm not hearing much (if any) change in the way of TONE while adjusting ONE of the L-Pads. I think perhaps for the time being, I'm going to leave well enough alone and just continue to use/listen to the Horn as it sits as I have to be in the right frame of mind to tackle this problem as it is a PITA job getting into the back of this Speaker as I have to (very carefully) lay this 175 lb. Speaker face down (on a thick folded up Comforter) to best access the back cover. Also the wiring is rather tight attached to the L-Pads so one can not just completely remove (or even lift too high) the cover without the possibility of yanking out a wire. At some point in the future, I will carefully remove the cover (and take LOTS of close up photographs) so I can be damn sure everything goes back in it's proper place. Still, for the life of me, I can't figure out how that Bass Driver is removed (kind of hard to explain without seeing).
    At any rate, I hope this old (sixty plus year old) Stephen Tru-Sonic Horn will hang in as I still enjoy it's sound (especially) with my new SET 2A3 Mono Amp.

    SixCats!
     
  6. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    I would try the 2A3 on another speaker, if the problem persists I would try new tubes in the 2A3 if they are older tubes in there now. Does the 2A3 amp have new caps in it? I have seen tube sockets cause this as well, you can try and wiggle the tube around in the socket slightly to see if it jumps back to a louder level.
     

     

    Please register to disable this ad.

  7. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    53,130
    Very likely IMO and IME with elderly loudspeakers' pots and pads.

    Here is some information on corrosion in a wire-wound potentiometer (rheostat). Now, this is a pot (rheostat) not an L-pad, but the basic construction values are analogous (only one variable section in a rheostat; two in an L-pad). This'll give you an idea of what you may dealing with.

    http://www.classicspeakerpages.net/...ing_the_ar-3a/restoring_the_ar-3a_full_pd.pdf (scroll to pp 13-14)

    [​IMG]
    source: http://audiokarma.org/forums/index....storation-guide-very-long-with-photos.306818/
    16 ohm L-pads are available, e.g., from PartsExpress and Madisound (probably numerous other vendors, too).

    Could be the tubes (direct heated filaments can be funny) or sockets (which can be 'retensioned' when necessary) but the symptoms don't strike me as quite right for either of these to be 'root causes'. More likely the driver (voltage amplifier) tube(s), I would think, given the symptom.

    If you have tubes you can swap into the amp (voltage amplifier tubes - 6SL7 IIRC? - or output tube -2A3), of course, swapping is always an excellent troubleshooting strategy.

    But (and strictly FWIW) I doubt it's the amp or the tubes.
    Full disclosure, this is more of a SWAG* than a statement of immutable fact! :p

    ________________
    *SWAG = Semi Wild-A$$ed Guess, in my lexicon.
     
  8. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Tubeglo,

    Thanks for the suggestion. I have tried the Mono SET 2A3 Amp on two other (Mono) Speakers and it appears to work/sound fine! The other two Speakers I tried are LESS sensitive than
    the Tru-Sonic Horn. One is my Brociner Back Load Corner Horn (housing a single 12" University 6201 Coaxial Driver) and the other a 15" Jensen Type "H" Concentric Driver in a Klipsch Short Horn. The (new to me) SET Amp was checked out by it's (former) owner and builder John Eastman here in Maine. John is an Electrical Engineer with lots of experience designing and building Amps. John said the Amp checked out well. I am leaning towards thinking that "perhaps", perhaps there might be an issue with one my (sixty plus year old) Tru-Sonic Horn's L-Pad. However, I was playing the SET Amp this morning with the Tru-Sonic Horn and, it's playing MUCH improved. The mystery continues!

    SixCats!
     
  9. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Mark,

    Thanks for the information you provided. I'm now going to "relax" (i.e. NOT panic like last night) and take my time and see how this all plays out.
    Funny, I played the SET Amp this morning on the Tru-Sonic and it now plays rather loud! I did (per above) clean/De-Oxit all four Tube Sockets last night which I figured couldn't hurt.
    Still, I'm leaning towards perhaps there being an issue with the old Tru-Sonic controls however, the question begs.....why (last night) would the 2A3 Amp play anemic volumes while the Pilot (EL84) sounded fine ?

    Oooh, I completely forgot about the "sticker" on the back of the Tru-Sonic Horn.

    103LX (#6165) Low Frequency Driver
    P 30 Driver (#912) for the ten cell
    825 Mid-Range Horn and a
    214 (#3283) eight cell Tweeter Horn.

    The ATTN: 5000X and 800X

    The ATTN's do NOT look like the one show in this (borrowed) photograph : [​IMG]


    I've been trying to find info./photos of my Tru-Sonic's ATTN with (thus far) no luck.

    Darn it, I SHOULD of taken photographs yesterday when I had the back cover off!


    SixCats!
     
    Last edited: Jan 12, 2019 at 12:20 PM
  10. primosounds

    primosounds Powered with pure tube sounds. Subscriber

    Messages:
    2,924
    Location:
    Terra, 21st century CE
    I believe you have contracted that dreaded disease, audiophilia nerviosa. It is characterized by inability to sit still and listen for more than 2 minutes before fussing with speaker placement, tone controls, balance, volume controls, tube rolling, etc, etc.
    Cure? vape some crypt sensimilla and wash down with your favorite brewski.
     
    gmfgmfgmf1 likes this.
  11. century tek

    century tek Super Member

    Messages:
    3,569
    Location:
    The Evergreen State
    You know, you could just temporarily bypass those L-pads to see what's going on. You're not going to blow some 10 or 20 watt speaker with a few watts or with normal listening levels.
     
    drtool likes this.

     

    Please register to disable this ad.

  12. mhardy6647

    mhardy6647 AK Subscriber Subscriber

    Messages:
    53,130
    That is true... although offing one of the Stephens drivers would be a traumatic event.
     
  13. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi guys,

    Primo, normally I would agree with you however, this SET Amp event the other night was "weird" to say the least. I can't explain what went wrong. That being said, today, the SET Amp appears to be working just fine and sounds very good. I've been playing/testing the Amp and other (Mono) Speakers all day (and now night) long. The "Volume" appears to be "normal" again. CT, I suppose I could do as you suggest however, per Mark's comment......traumatic event would be the understatement of the year should something go wrong. Man, I can not believe the prices for Stephens Tru-Sonic parts! YIKES! I saw the P-30 Driver (for the ten cell Mid-range Horn) listed at a grand today. Just the Driver! Oooh, using one of my powerful Flashlights, I could see into and inspected (right through the Screen) the Attenuator's and thankfully, I saw NO disconnected wiring so, at least there's that. Primo, I did in fact listen to a LOT of Music all day long. Just played some "Monk" for the last hour. Also really enjoyed Angelo Badalamenti "Twin Peaks" Sound Track on the Tru-Sonic. System played PLENTY loud! Thanks all for your help and suggestions. Time for some food and later, a BOURBON!

    SixCats!
     
  14. mkane

    mkane AK Subscriber Subscriber

    Messages:
    6,551
    Location:
    103 miles N. of S.F.
    so much for de-ox on L-pads.
     
  15. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Mkane,

    Well, I was informed that L-Pads are not the correct term. I guess they are more accurately called Attenuators.
    That being said, yes, me thinks I'll not spray De-Oxit into the Attenuators again. Now, I can't say for sure my having
    sprayed the Attenuators was the cause of the problem (one wouldn't think so) but, who knows when it comes
    to a sixty plus year old Speaker. So far, all "appears" to be back to normal with the Tru-Sonic and the SET 2A3 Mono Amp.


    HA! Well, I'll be a Monkey's Uncle! I just now found this pix/link on the Net. This pretty much confirms what I have long suspected,
    that is to say, in the last year or so, I had finally come to the conclusion that my Tru-Sonic Horn must be either a "Custom" model or (per this link)
    a rare PROTOTYPE Speaker! I have never seen another Tru-Sonic Speaker exactly the same as the one I own so, I'm going with PROTOTYPE.
    This link/photo/provide information is the first Tru-Sonic Protoype Speaker I've seen that has the exact same WIDTH as my Speaker : 36 inches
    where as the E3 Model (which houses all the same Drivers) is four inches less wide (32" W).


    https://www.1stdibs.com/furniture/tables/end-tables/charles-eames-prototype-speaker/id-f_247802/

    Charles Eames Prototype Speaker :
    About
    In the late 1950s, the Stephens Trusonic company produced high quality monophonic speakers designed by the Eames Office. The production speakers are very rare today, but this experimental example is a unique prototype. According to Don Albinson, Charles Eames' close associate for decades, "a number of different designs for speaker enclosures were made and most of them were on Herman Miller pedestal bases. This one was put on four cast legs because of its size and shape. The legs were actually a George Nelson design but George okayed their use on this speaker cabinet." A very pure and architectural object, this museum-quality piece still functions as a speaker but is equally useful as an unusual table.
    [​IMG]


    upload_2019-1-12_21-51-21.jpeg
    The above is my Stephens Tru-Sonic. Mine does NOT have the retractable Horn like the E3 shown below.


    [​IMG]
    E3 Model

    Regards,

    SixCats!
     
  16. Selmerdave

    Selmerdave Well-Known Member

    Messages:
    825
    Deoxit does take some time to dry out...
     
    Last edited: Jan 13, 2019 at 9:27 AM
    gmfgmfgmf1 likes this.

     

    Please register to disable this ad.

  17. Drugolf

    Drugolf AK Subscriber Subscriber

    Messages:
    4,634
    Location:
    Boise
    Deoxit was still wet in there I bet. Didn't sound like you let it dry long enough. Try blowing them out with compressed air. ?
     
  18. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Guys,

    Yea, I realize it takes a little time for De-Oxit to dry out but, supposedly it's listed as a quick drying formula. That being said, I in fact waited several hours before attempting to play the Amp & Speaker. I may never know just what the heck happened in this situation. Perhaps my having De-Oxit the Amp's four sockets (and cleaning Pins) had a positive effect ?

    SixCats!
     
  19. Tubeglowpio

    Tubeglowpio Active Member

    Messages:
    387
    Location:
    AZ
    I would just replace the pots, sometime deoxit and working the pot buys you some time but it's best to just replace it and not have to worry about it.
     
  20. SixCats!

    SixCats! Super Member

    Messages:
    2,541
    Location:
    Maine
    Hi Tubeglow,

    Yea, I'm thinking you are correct (and at some point in the future when time permits) I very well may do just as you suggested.

    For the time being, I'm not going to mess with the Horn since everything appears to be working fine/back to normal volume. Thanks.

    SixCats!
     

Share This Page