| Author | Message | ||
| Denver |
Hi, I have a 210HD 130 watt. It didn't work when I got it- You could turn the power on, light came on, but as soon as you tried to take it off stand by (in either direction)the fuse would blow. I narrowed it down to the diode on the 4th tube (closest to the edge) and replaced it.(I beleive that this is a freewheeling diode to reduce inductive kick on shut down). Now I have sound, but I cannot get a nice clean tone. Nor very much volume. Oh yeah, the tubes on the high setting get really hot, like the whole damn thing glows red. I have never seen this before. Thanks, Denver | ||
| mike kaus |
First off, does it have a 12ax7 Phase Iverter? If yes, you have bias trouble probably. If no, it's in the driver transistors most likely. Do ALL four EL's go red? It really sounds like you lost control grid voltage. If yo have a 12ax7, check the voltage on pin 5 with the tubes out. It should be negative voltage. There is a pot on the main circuit board for adjusting this. You need MORE negative. | ||
| Denver |
Hi Mike, Thanks for responding so fast. This does not have a 12ax7 tube in it. | ||
| Denver |
All the el 34s glow red. | ||
| mike kaus |
Well, you. lost the driver section somehow. You'll have to check the driver board most likely. It has a couple of big heat sinks and to-220 sized devices, an IC and about 5 small electrolytic caps, any of which could be causing the problem. Could be a bad resistor an the same board.. Go to the adjustments thread(oh wait a minute-this IS that thread!) and poke around to find the procedure for adjuting the driver board on db-2 model. That will give you the parameters for the output transistor. If yo are not able to get those balanced or have no outpput control, you're on th right track. | ||
| Denver |
Hi Mike. Thank you for the help. I will do some digging and see what I can find. I will post again when I fix it, or when I get stumped. Thanks again, its really nice to find this website where people who really know their stuff take the time to help out others. cheers. | ||
| Denver |
Okay, checking the bias across the 3.9 ohm resistors. 12mV and 20mV. And that is cranked right up. It was at obout 5 and 11. I now have more vol and sustain, but still distorted. If you know what might cuase this low bias let me know. Also it is the same when on standby and lo setting (as well as high) is this normal? I will keep looking at the driver board, but let me know if anything jumps out at you. Thanks, Denver | ||
| Denver |
it also has NTE196 transistors in it. Are they original? I am not sure what has been done to this amp in the past. | ||
| Denver |
Sorry, they are ECG 196 transistors, my bad. | ||
| Denver |
plate voltage is 698V. I just keep adding this stuff as it comes, I guess I don't have enough brain capacity right now to think of everything at once. | ||
| Denver |
Okay, here is all the info. Plate voltage- 698 on Hi, 460 on low. The 16V line seems fine, the50V line seems fine. Grid- 355V on Hi, 260V on lo. I traced all the way thrugh the driver board, there are no dead ends, it all makes sense. 1.236V going into bias trimpot, 1.236V coming out of bias trimpot. I still only have 11mV on one 3.9, and 20mV on the other. Diodes on driver board seem to check out fine. Here are the voltages on the transistors (ECG 196) Center pin 50V, Right pin 0.606V, Left pin 11mV and 20mV. On my 1458 I do have a +16V and a - 16V. I think I might look at the pre amp at the common points for both channels. The amp does have some volume, but nothing like described like others on this site. To sit and play you have to have gain to 5, and master to 10. That is with all tones up to 5. It has an odd distortion and decays quickly- not much sustain. When you do a cap job, do you do all the caps? (blues, yellows and discs)? Or just the 9 blues? Also, could it be anything to do with the lm307s? Or something as simple as the master volume pot? Thanks for reading, Denver | ||
| Denver |
Just a reminder- this is a 1979 210hd 130. No 12ax7 tube, switching from hi to lo only changes 700 and 350V levels, no control levels. Heaters come off primary side of xformer. | ||
| Denver |
I swapped the lm307h's around, no change. And I have tried a different speaker cab with a different cord, different guitars with different cords, nochange. I pulled out the 1458, checked connections, put back in, no change. Bypassed master vol, no change. Must be transistors or caps? | ||
| Denver |
Just looking over my last 8 posts. I'm a little long winded, sorry folks. Denver | ||
| mike kaus |
HMMMM-had the same problem with a 130 that I converted to SS driver with a kit from MM back i the day. Never DID get that one straigt. Went back and put it back to tube driver and then blew it up! Seems to me the bias reading come up positive on pin five if read to ground wit the solid tate drive as the cathode is only negative in relationship to the anode. I still have to believe that your problem is in the JE1692 driver transistors. It's a cathode driven amp so everything is backwards with the cathode being driven off of the 1692 and positive voltage being applied at pin 5. I think Steve Kennedy is more versed in the SS driver than I am but I still would look at the1692's. I can't see anything in the circuit that would cause the condition other than that. | ||
| Denver |
Thanks Mike. I tried to cross reference the JE1692 at the local electronics wholesale. He couldn't find it. I know that there are suggestions else where on the website, but is there one that you favor as a replacement? Denver | ||
| Denver |
pin 5 to ground is +15V | ||
| mkaus |
On all four tubes? | ||
| Denver |
Yes, on all four. That seems out of whack compared to what I've seen on this site. | ||
| Denver |
I ordered a couple 2n6488's today, so in a couple days, maybe that will fix it. The guy at the store said that 2n6488 cross refs with nte331, so I don't know why I have ecg196 (the same as nte196) in this amp, possibly the guy before me made a guess. Thanks, Denver | ||
| mike kaus |
Let me know, I'm curious. I'm sure the transistors have to be biased wrong to cause the distortion and low volumes. That's the only thing that makes sense. Mike. | ||
| Denver |
Hi, I just swapped out the transistors. Now I can adjust the bias to whatever. I biased it to 23mV and was excited to try it out.....no change! Its wierd. As I mentioned before, the highest I could get my Bias was 11 and 20. Now they are both at 23, and the dial is in about the center of its rotation. I was pretty sure that a change like this should change the sound. But it didn't. I am starting to get stumped. Denver | ||
| Denver |
Also, the deep switch does not seem to do anything. I ohmed it out, it goes straight through when you turn it on, so its good. I just thought that maybe this could be an indication of something else. Denver | ||
| Denver |
I recapped the driver board, still no change. | ||
| mike kaus |
I have to assume now that you are going to have to verify that the signal is distorting only in the final. You are going to have to scope it and look to see that the distortion isn't coming from the front end. I don't know any other way other than to follow tha signal through with a scope and see where it starts to break up. I'm almost inclined to think maybe the signal coming out of IC8 is either distorted or overdriving the tubes. It could be the LM1458 is overdriven and distorting. but you'll have to get somebody who understands IC's better than me to figure out how to lower/clean up it's output. I'll be REALLY interested to find out what this one is. Pin 5 voltage is still a form of control grid voltage- you MIGHT try altering it slightly up and down to see what effect it has. It appears to feed two 220 ohm resistors after leaving a 1k-2w per pair. | ||
| mike kaus |
Posted a request over on the weber board for some help. There are some pretty smart guys over there too> Mike. | ||
| mike kaus |
I also email somebody who is in the business and got his opinion. This guy is repected all over the world so this isn't idle poop. Here's his response:: Mike, Poor guy has waded into a real snake pit. Common Cathode amps are very hard to understand. Advice: (or what I'd do), This is gonna take an O-Scope and experience Remove power tubes and look at the input to the Phase Inverter transistors. (TIP31C is the accepted sub for the 1692.) Is it a sine wave? If sine wave there, go to the grids on the output tubes. If it's distorted strat tracking back thru the pre-amp. BE sure all the voltages check-out for the output tubes. It may be a bad output transformer. I've seen the damper diodes leak or go shorted on the output tubes. Also seen the ceramic caps leak or short. Usually takes out output tranny. | ||
| Denver |
Thanks Mike, I will try all that and post my findings. Denver | ||
| Denver |
Hi Mike. Just wondering if you had a list of all the voltages on all the pins of the output tubes? I personally don't have a scope, but we do at the college ( I am taking 4th year electrical), so I will bring the amp in with me if I don't figure it out first. After all this, I am thinking of taking some electronics courses, its pretty complex stuff when you get this far into it. Thanks again, Denver | ||
| mike kaus |
The only voltages that I have on the schematic are 350v@ pin four and 700v at the input center tap of the OT and the 16v lines of course. I don't HAVE one of those SS amp so I'm going strictly off of the schem. | ||
| Denver |
Thanks Mike. Does anyone know the ohmic values for the primary windings of the output tranny? That is from the red to the blue and the brown, should they be the same? The schematic shows the red as a true center tap. Thanks, Denver | ||
| Problem Solver |
If you cant fix it, can I have first dibs on all your music man name tags?...  |
Tue, 03/25/2014 - 09:28
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