| Author | Message | ||
     Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
210HD export: voltage service ZENER out of service ?. My amp is a 210HD 130 (2275-130EX, N° BO07386). Transformers were built in 1977, and speakers in 1978. It has a SS driver, but some elements from tube driver. For example I have the two 20µF/450V in the box (listed in tube driver schematic, not in the SS driver schematic) as well as the small transformer. I bought it in France in spring 1980 as new . Soon after I got a problem (blow a speaker, and tubes) most probably because of using it at distortion mode at high power switch). There was no service on this amp since 1980 and 2 weeks ago I started some maintenance. I change the tubes and the 4 main caps (in the box) and recover original sound with plenty of bass and headroom but and after running 1 hour with standby on and no input signal, the amps is now humming, with no more sound when I plug a guitar. Power amp seems OK (voltage at 3.9 ohm resistors in SS driver are 25mV and 34mV, plate voltage is 770V high, 518V low postion switch (as it has always been, too high ?). I measure 15.5 V at pin five of output tubes, and 259/377 V (low/ high position switch) at pin 4 , normal ? I think I found the problem. I should have +16, -16V at preamp through the 2 zener 4745 (D5 and D6). I measure almost 0 at one and –4 at the other. Connections of these diodes are blueish and probably got very hot (see red arrows on photo). At R44/C31 and R46/C32, I measure +47 and 48 V respectively. Is it normal input voltage for the zeners ? The other zener 1N4745 (D17) in ss driver have its connection blueish and probably got very hot as well. I have to order some (with higher wattage ???), I am sure they are connected with my pb, agree ? what could be the cause of these failure (caps 25µF or the 150 µF , too much voltage due to 237V input) ? I would like to put here some interesting photos that stated I have a DB 2 SS driver and GB-1B preamp as seen on the reverse side of the circuits. What is the meaning of the e@/3 logo on the reverse side of the circuits ? how to insert photos ? The reverb as always sounded awfull compare to a typical twin reverb amp. From this forum I understood that reverb could sound nice in MM amps. I’d like to get it well sounded, Any idea ? the reverb unit work OK in a twin reverb, my second amp. Thank’s for comments, do other export 2275-130 EX behave the same ? Vignau | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Sorry I didn't see this earlier. I'm not sure why you have such high voltage on low since that was the idea behind it was to lower overall voltage. I woould suggest replacing those burned up zenar, if they are and firing it up. I don't really remember what the voltages are supposed to be and don't have a schem in front of me but those appear to only be on the ic supply side so they shouldn't affect the high side voltage. Don't know what the e@3 logo means. Personally, I always felt th eMM reverb was pretty nice but i dthe voltages are all screwed up, no telling what it wil sound like. I'm sorry I can't be of more help but it MAY have a low side out o n thetransformer and giving you high voltage. Not sure. It make take a lot of investigating to work through THIS much. Mike. | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
Salut, Christophe! If you measure +/- 48V at the R44/C31 and R46/C32 junctions, your input voltages are ok but your zeners are dead. Check the 620ohm resistors (R44 and R46). If you haven't changed the 150uF caps (C31/C32), now is the time to do it. If you can, get 63V ones instead of the 50V as this gives you a better safety margin. 15.5V (nominal voltage is 16V) on the EL-34 grids at rest is fine. 377V on the EL-34 screens is a wee bit high - but it's dependent on the B+ voltage. 700V B+ should yield 350V for the screens. Measure the high B+ and check your 150k bleed resistors too (as usual, all the usual caveats about working on high voltage equipment apply). Hope this gives you something to start with. -Lars Verholt www.captain-foldback.com | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Hi Mike and Lars, Thank’s for the answers. I appreciate opinion. This site is really great. This is now the situation: All the caps (150µF, 25µF) have been changed, 63V for the 150µF as 50 is not available anymore anyway. Zeners D5 and D6 changed. Problem is remaining. Maybe I fried the new zeners. R44/46 goes quite hot (I would say 70°C (158 °F). I measure both them at 670 ohm instead of 620 (almost 10% more, does not seem too bad for me). 150K bleed resistors (R16 and R67) were measured at 165K and 170K (almost 10% more, does not seem too bad for me). B+ is 522V on low and 770V on high. Input AC voltage is 235V Voltage measurements on tubes sockets were done without the tubes. Same voltage were observed on the 4 tubes with below’s values (high/low position): Plate: 772/522 Cathode: almost 0 with the scale I used. Grids: 16/16 Screen: 392/261 I have the feeling my problem is not linked with these quite high voltage, it has probably always been like that, I just change the filter caps and put new JJE34L before problem occur. The neon bulb does not light, is it normal, could there be a link ? If this is a zener problem then there is something that fries them. Other suggestion, from my brother who experience similar situation on fender’s. A bad/cold solder joints. He is convince this is THE problem. It seems to me problem is located in preamp section, so: bad component, solder problem, neon bulb ? Other possibilities ? Thank’s for all your precious comments | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Voltages taken with the tubes out WILL be higher. You need them with the tubes running. Neon bulb could just be burned out. The zenars get hot. That voltage disipation has to go somewhere! I guess we need to know, what exactly IS your problem? just the reverb sounding bad or something else? No signal through it still and humming? I think you may just have a signal path out. You'll have to trace it through from the start to see where it goeas out. | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Mike, reverb problem is a secondary problem that always occurs since I got this amp in 1980 brand new. The exact problem I have now is no sound when I put signal on input, only hum. I will go back measuring voltage with tube on, that was Steve who told me to measure voltage with tubes out. I don't understand exactly what you mean by " a signal path out". Christophe | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Mike, reverb problem is a secondary problem that always occurs since I got this amp in 1980 brand new. The exact problem I have now is no sound when I put signal on input, only hum. I will go back measuring voltage with tube on, that was Steve who told me to measure voltage with tubes out. I don't understand exactly what you mean by " a signal path out". Christophe | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Mike, here are voltages on tubes sockets with tubes on place (high/low): Plate: 768/511 Cathode: 55/40. Grids: 16/16 Screen: 383/254 not so different... I'm still trying to trace where/why signal is lost and hum generated. Christophe | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
You might try getting an audio probe. I don't use one but I've got a scope. These allow you to touch points along the signal path and run it to a separate amp to see if you have signal getting through. Here's one place but I'm sure there are more. http://www.singlecoil.com/helpers.php | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
By the way, here's how you can build your own. Mike. http://www.diyguitarist.com/PDF_Files/DI Y-AudioTester.pdf | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Thank's Mike, I will go on and get all inform, I just need to spend some time on it. Christophe | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
Your output stage voltages appear to be ok, if little high. If you are still getting +-48V where you should have +-16V, your zeners are open (or there are bad connections). If you get no signal on either input channel, IC-8 or IC-7 (or both of course) may be bad. You can verify which it is by injecting signal from an iPod at the 'deep' switch. If you get no sound in the speaker there, IC-8 or C-34 are bad. Hope this helps -Lars Mikael Verholt www.captain-foldback.com | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Mike and Lars, something I do not understand, why tracing signal if there is no +16/-16 at zener output ? IC will not work anyway if not powered, right ? Then should I focus the problem on power side or shortcircuit around the zeners ? Christophe | ||
| Lars Verholt (lmv) Username: lmv Registered: 11-2009 |
Power first, then signal. -Lars Verholt | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Lars be right-no power, no worky. THEN look for other problems. I sometimes jump ahead too many steps. I'm too used to being THERE! | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
I Lars and Mike, after several month, I found some time to come back on my amp. I found something interresting: When I remove IC8 (located on phase inverter board), I recover the +16 -16 at zeners. Could this IC being in short circuit or might it be something else around it ? Did you experienced pb with this IC8 (LM1458N). I already order a new one , I 'll let you know but your input could help/confirm. Christophe | ||
| Christophe Le Crom (vignau) Username: vignau Registered: 08-2010 |
Lars and Mike, Bingo, that was the LM1458N OP in short. With new one everything went back to order... Just need now to get a better reverb, I'll change the spring box. Thank's for all your advices, I will keep in touch.Christophe |