Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SleepLess on September 22, 2012, 06:16:51 am
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Hi.
I have just finished placing all the resistors and caps on the fibeboard but for one thing: the 10M resistor soldered on the lower left leg of the optoisolator. I don't have any 10M resistor, all I have is a 8M2 and some 1M and 2M2. Can I just solder the 8M2 instead or must I really place a 10M there? What would be the consequences of soldering a lower resistance there?
Gut shots will come in due time... :icon_biggrin:
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Put the 8M2 in series with a 2M2, and you will be within the 10% tolerance.
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or measure the 8M2, it might be close to 10, anyway a 9M would be just fine in there
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Thanks a lot guys!
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One question guys... I have a brass grounding plate that I have installed and intend to use as a grounding scheme. The thing is that upon viewing 1960's models the pots are grounded to the brass plate from the left lug to the plate. But is that really necessary as the pot is already actually grounded through the mechanical connection between the pot and plate? Must I really add that extra grounding wire?
Thanks!
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I have a brass grounding plate that I have installed and intend to use as a grounding scheme. The thing is that upon viewing 1960's models the pots are grounded to the brass plate from the left lug to the plate. But is that really necessary as the pot is already actually grounded through the mechanical connection between the pot and plate? Must I really add that extra grounding wire?
I haven't seen the insides of many original '60s Fender amps, but I don't recall a separate ground wire for the pots. I remember the lug being bent over and soldered directly to the pot body. Then the pot nut/washer make a mechanical connection to the brass plate. That arrangement has caused a lot of booger grounding problems.
I would use a separate wire from the pot lug directly soldered to the brass plate just to avoid relying on the mechanical connection of the pot body. And I woulduse a wire to connect the brass plate directly to the filter caps rather than rely on the mechanical connection between the brass plate and chassis. Many times different metals in contact will cause a galvanic reaction that will corrode and cause a poor electrical connection. Here's a pic of a '64 DR that clearly shows Fender's grounding plate. Again, I don't recommend this method.
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Look... This one has been modded (strange things going on with the bias pot there!!!) but you can see the black grounding wires going down from the pots to the plate.
I intended to ground the filter caps to a PT ground lug along with the HV CT and HT CT.
(http://imageshack.us/a/img210/3430/1968superreverbinsides.jpg)
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That amp is a later model Silverface AB568. That bias is the stock balance type. And those big ole 150Ω/7W resistors on the output tube cathodes are also stock. Same for the 2000pF caps on the grids.
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Yes, it's from 1968.
But I see the filter caps are grounded to a PT bolt and the pots to the brass plate. Can I implement this or do you recommend to get rid of the brass plate and install a floating buss bar instead? :dontknow:
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I prefer the bus bar but if you build in a shallow slope faced Fender style chassis, there may not be enough room. The brass plate is fine if it is securely connected to the chassis. I don't like to rely on the pot nuts for a ground though. Too easy to loosen. This is all opinion and there are several methods that have worked well for decades.
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OK guys. The amp is finished. That was a long job!!! I just need to wire the cabinet and of course recheck everything one last time before firing it up. There's just one thing I'm not totally confident about, it's my AC switch / fuse wiring.
Here's what I did with the MM PT Toneclone FBFS-P40/100-240 which as a dual primary. This made me end up with a brown wire and a white wire to use. The brown one is OV (COM) and the white one is 240V. So I soldered the brown one to the AC switch and the white 240V to the side of the fuse. Then the AC cord has its black wire to the center lug of the fuse holder and the Neutral white to the AC switch. I don't know if that's 100% correct and if I'm not missing a connection there...
Now gut shots, if you see anything strange, just say so. I plan to fire it up tomorrow.
(http://imageshack.us/a/img856/8724/mg3214.jpg)
(http://imageshack.us/a/img41/9701/mg3215g.jpg)
(http://imageshack.us/a/img96/2103/mg3218m.jpg)
(http://imageshack.us/a/img823/2553/mg3206.jpg)
(http://imageshack.us/a/img717/6269/mg3213r.jpg)
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Just in case you'd need it to help me sort out that fuse /ac switch wiring here's the PT schematic, I wired it for 240V operation:
Thanks!
(http://imageshack.us/a/img191/1124/transfomm.jpg)
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Nice work! That looks very neat and tidy.Well done!
Where did you get that thick cloth wire from?Looks cool.
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Thanks!!!
Got it from Antique Electronic. But let me tell you it's a freakin' pain in the... to work with. It doesn't pull back and the wire stripper doesn't work with this, I had to cut each wire end with a cutter...
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I have reversed the white and brown wires. Com now goes to the side of the fuse and 240V goes to the AC switch.
Switched the ON/OFF switch ON without tubes and checked the ac hot lug I have 232V. All the heaters are at 3.21 VAC.
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Beautiful! Very nice twisted pairs too!
Brad :bravo1:
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Where did you get that thick cloth wire from?Looks cool.
Got it from Antique Electronic. But let me tell you it's a freakin' pain in the... to work with. It doesn't pull back and the wire stripper doesn't work with this, I had to cut each wire end with a cutter...
Yes, I would strongly advise to use Doug's cloth wire over the AES "cloth covered" wire. The AES product is regular PVC insulation with a non-waxed cloth cover over that.
As Sleepless mentions, you can't do the push-back technique with it. Further, the cloth cover is a lot like a shoelace, and its weave will loosen and fray where it is cut. Without a lot of care (or your own applied wax), it will give a poor-looking result. None of these problems with Doug's wire.
I've got a bunch of spools of the AES stuff, which I foolishly bought in bulk before seeing this wire in person. If I haven't already trashed it, the wire is just sitting around because it's too much of a pain to get a professional finish with it.
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I've got a bunch of spools of the AES stuff, which I foolishly bought in bulk before seeing this wire in person. If I haven't already trashed it, the wire is just sitting around because it's too much of a pain to get a professional finish with it.
Absolutely... Bought it in 50ft spools too... Dang... They'll get trashed or will sit around as well...
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Yeah, Nice job. :icon_biggrin:
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Thanks but dang... It's not working at all... I get correct readings but no sound at all... :BangHead:
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When did that happen? Wasn't it working before?
Brad :w2:
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I've got a bunch of spools of the AES stuff, which I foolishly bought in bulk before seeing this wire in person. If I haven't already trashed it, the wire is just sitting around because it's too much of a pain to get a professional finish with it.
Absolutely... Bought it in 50ft spools too... Dang... They'll get trashed or will sit around as well...
I did the same thing, ordered a bunch of the wire and now it sits unused.
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When did that happen? Wasn't it working before?
Brad :w2:
NO, all I did before was turning it ON (left the stdby ON) without tubes just in order to check the heaters. They are good.
Today I inserted all the preamp tubes and everything went OK.
Then I inserted the 6L6GC and turned it ON. I have -60V at the bias pot, 470V B+ where it should. But I have absolutely no sound at all... :BangHead:
Here's one thing I'm thinking about and I'd like you to tell me what you think as this is most puzzling to me... The MM OT schematic shows two different wiring possibilities which is most confusing. I love that stuff... "Wire it as such and if your OT blows, well bad luck, you had to wire it the other way..." Check this joke out, I chose the second method with black as COM and green as 2 ohms, and if that's the wrong choice what happens? Blows the OT? Or no sound at all as I'm currently experiencing? Thanks!
(http://imageshack.us/a/img855/277/mmotm.jpg)
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But I have absolutely no sound at all...
Divide and conquer....
With tubes in you are not getting any sound?
If so, try poking on control grid pin 5 of power tubes...there should be some noise...work you way towards input touching control grids from PI, rev recover, rev drive, input tube... Noise generated will be gradually louder each time you hit a previous stage on amp design.
Also, your bias point -60V seems too low...try to measure mV on 1ohm cathode resistors and write down how much current is getting thru the bottles...
Hth
Best Regards
R.
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But I have absolutely no sound at all...
Divide and conquer....
With tubes in you are not getting any sound?
If so, try poking on control grid pin 5 of power tubes...there should be some noise...work you way towards input touching control grids from PI, rev recover, rev drive, input tube... Noise generated will be gradually louder each time you hit a previous stage on amp design.
Also, your bias point -60V seems too low...try to measure mV on 1ohm cathode resistors and write down how much current is getting thru the bottles...
Hth
Best Regards
R.
OK will do that. I have -66 V on the 10KL bias pot down to -47V when turned up full...
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OK.
I reversed the black and green OT wires and I still don't have any sound...
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Usually it's the input or output jacks that get miswired on builds like yours.
If ALL the voltage are right then that's where I would look.
Reversing the OT leads is only useful in the event that the amps squeals when turned on.
What are the control grid voltages on the preamp tubes?
These wire strippers will work on that kind of wire.
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You can try this, unplug the reverb output that goes to the verb tanks input. Hook up a 8 ohm speaker to that verb output RCA jack and see if you get any sound out of it with your guitar pluged in to the amps input jacks. If you do then you know it's after that point in the amp that's not right.
Brad :icon_biggrin:
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Voltage chart guys.
Heater voltages are all at 3.1VAC. All measures taken in DC.
Tube
Pin V1 V2 V3 V4 V5 V6 V7 V8 V9
1 182 273 463 289 459 266 -63 -63
2 0 0 0 0 -46 63 470
3 1.15 1.98 9.6 1.93 0 103 471 471
4 469 469 356VAC
5 -63 -63
6 239 288 465 291 400 253 469 469 356VAC
7 1.3 0 0.4 0 -48 69
8 1.3 2.3 9.6 1.9 0 103 0 0 470
Strange to have 0V on pins 4 and 6 of the rectifier right?
Thanks for your help guys!
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All measures taken in DC.
Pins 4/6 on the rec. tube will be AC, did you have your meter set for AC?
Brad :think1:
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The rectifier pins are measured in AC volts.They get rectified to DC at pin 8.
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:BangHead:
Rectifier pins 4 and 6 are 356V AC...
I'll edit my voltage chart!
Thanks Brad, this one is making me lose my mind!
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Lets see some closeups of your output jacks and input jacks.
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He has -63dcv for bias.
Is that enough to bias the output tubes into full cut off?
Brad :think1:
Edit; Nope I'm wrong, Fender schemo says -52dcv for bias.
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Lets see some closeups of your output jacks and input jacks.
I hope these will be good enough. Say so if you need other angles or anything else... And thanks already!
(http://imageshack.us/a/img821/6724/mg3225.jpg)
(http://imageshack.us/a/img109/7788/mg3226.jpg)
(http://imageshack.us/a/img715/3382/mg3227.jpg)
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Are the green and black wires from the OPT reversed on the jack? I always thought black was to go to ground?
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Are the green and black wires from the OPT reversed on the jack? I always thought black was to go to ground?
Yes, that's what I wrote in an earlier post. I reversed them to check if I'd get any sound because of the OT's schematic which shows two possible wiring configurations (thanks MM!). I had them reversed before and didn't have any sound eitherl...
So if I understand correctly my voltage chart is good and my inputs and outputs are good... So what the hell could it be... :cussing:
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OK. One more voltage chart as I have some differences now, particularly on V1 pin 7 where I now have 0V and on V1 pin 6 where I now have 298V instead of 239V and also on pin 8 where I have 1.89 instead of 1.3. I also now have some voltage on pin 2 of V3 where I had 0V before... I set the bias hotter (tubes biased at 39mA for V8 and 34mA for V7). I have -51V on the bias pot middle lug and my B+ is 451V.
All heater voltages are still at 3.1VAC.
Tube
Pin V1 V2 V3 V4 V5 V6 V7 V8 V9
1 180 267 451 282 447 259 -50 -50
2 0 0 1.4 0 -46 61 456
3 1.15 1.95 9.7 1.88 0 100 455 4551
4 454 454 358VAC
5 -50 -50
6 298 260 450 283 387 243 454 454 358VAC
7 0 0 0.5 0 -48 68
8 1.89 1.89 9.6 1.9 0 100 0 0 457
I'm lost. I need your help...
Thanks!
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But I have absolutely no sound at all...
Divide and conquer....
With tubes in you are not getting any sound?
If so, try poking on control grid pin 5 of power tubes...there should be some noise...work you way towards input touching control grids from PI, rev recover, rev drive, input tube... Noise generated will be gradually louder each time you hit a previous stage on amp design.
Also, your bias point -60V seems too low...try to measure mV on 1ohm cathode resistors and write down how much current is getting thru the bottles...
Hth
Best Regards
R.
I did all this and poked everywhere with a chopstick. No sound at all. The amp is as quiet as a church mouse even with all knobs on 10...
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You can try this, unplug the reverb output that goes to the verb tanks input. Hook up a 8 ohm speaker to that verb output RCA jack and see if you get any sound out of it with your guitar pluged in to the amps input jacks. If you do then you know it's after that point in the amp that's not right.
Did you try this?
It will tell you if it's pre or post of the reverb. Help you narrow down where to look.
Brad :icon_biggrin:
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No I didn't willabe, I don't have any RCA to 1/4" jack converter... If I understood what you said correctly... Thanks!
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Yes I think you understand.
You could use jumpers. You only need to see if you get any sound for a few seconds.
Brad :icon_biggrin:
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I can't do that test Willabe... I don't have the needed tools (jumpers). I have reversed the white and brown wires from the PT, the ones that go to the side of the fuse and the AC switch and to my surprise the amp reacts just as it does with these wires wired the opposite way.
The amp reacts on standby exactly like it reacts off standby. Except that the readings change of course. No sound... :BangHead:
I think I'd rather have a noisy amp than a silent amp. At least a noise is easier to locate and fix... What can you do when the amp remains silent all the time. I stuck a stick on each eyelet, each pin, each wire and nothing, absolutely nothing... I'm totally stumped...
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Ok, 1 last thing you could try.
If you have an extra 1/4" jack you could temp it in in place of the RCA verb send jack. It's only 2 wires. You don't even have to take the RCA out of the chassis.
The guys always say "divide and conquer". This will split/divide the amps circuit in half.
I'm gonna write Santa a letter and ask him to bring you some jumpers for Christmas.
Brad :laugh:
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OK. Now comes another big debugging phase...
The problem was the speaker jack which had a short. I used another jack to connect the amp to my 8 ohm 1X12 cabinet and the amp made a noise. I changed the speaker jack on the SUper Reverb and now I'm getting a sound. BUT:
1. The amp is far from being as loud (and good sounding) as it should. On 7 its volume is like it was on 1.5!
2. The reverb creates a massive increasing hum past 3 on the knob so I have to turn it down.
3. Tremolo works but only if the reverb pot goes past 3. Below that I don't have the effect coming out of the amp, I just hear the oscillation ticking through the speakers. This suggests a bad tremolo/reverb pots wiring but I have checked them and they are wired as they should.
4. I replaced V3 with another tube and nothing changed.
5. The Normal channel volume pot is scratchy as hell and even emits booms when I turn it up, especially between 8 and 10... Changed V1 and I have the same symptoms
At least now I have some sound..; But I still need you guys!
This freakin' amp is a nightmare...
Thanks!
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Hey guys.. I LIKE the wire you're talking about from AES... send it all to me, I'll pay the postage !.. no kidding !
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Hey guys.. I LIKE the wire you're talking about from AES... send it all to me, I'll pay the postage !.. no kidding !
You must be kidding! This wire is utter crap to work with.
Oh and btw if you have any ideas about this SR issues... :icon_biggrin:
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Try cleaning that volume pot with a good spray cleaner. If its still scratchy there is unwanted DC voltage on that pot (Leaking coupling cap). Check your reverb cables for shorts and continuity. Can you measure your power tube cathodes to see how much currant they are drawing?
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Try cleaning that volume pot with a good spray cleaner. If its still scratchy there is unwanted DC voltage on that pot (Leaking coupling cap). Check your reverb cables for shorts and continuity. Can you measure your power tube cathodes to see how much currant they are drawing?
Thanks a lot for your help.
I have got some WD-40, can I use it to clean the pot or not? OK about the leaking cap, I'll see after cleaning the pot.
The reverb cables I have are brand new and out of the package. New style.
The 6L6 cathodes are at 0V (posted earlier in my last tube voltage chart). If you're talking about the bias they are at 39mA for V8 and 34mA for V7. I tried those tubes in another amp and they work well despite the unperfect match. Or are you talking about something else? Power tubes cathodes are pins 8 right?
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I would not use WD40. Do you have a Radio shack, Electronic Parts store or Home Depot near you? They have contact cleaner spray that is ideal for cleaning pots. Clean all the pots while your at it.
Just because something is new does not make it perfect, QC now a days is in the toilet.
Yes, pin 8 is the cathode on a 6L6. What did you use to get those mA readings?
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I would not use WD40. Do you have a Radio shack, Electronic Parts store or Home Depot near you? They have contact cleaner spray that is ideal for cleaning pots. Clean all the pots while your at it.
Just because something is new does not make it perfect, QC now a days is in the toilet.
Yes, pin 8 is the cathode on a 6L6. What did you use to get those mA readings?
OK. I used Doug Hoffman's bias checker that I built two or three years ago to get my mA readings.
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Guys:
1. I have tested every wire and every eyelet with my MM continuity checker and everything's good.
2. I have 10VDC on the normal channel pots to ground. It seems to start from the volume pot and then spreads out to the two other pots thanks to the jumpers. Can you tell me how I can fix that? Do I randomly change the sozo caps from right to left or is there a particular one I can aim at straight away?
Thanks...
Once the normal channel noise will be fixed then we'll have the overall volume issue tu fix and the reverb issue as well. Or maybe the first fix will cure it all??? :think1:
UPDATE:
I changed the first .1uF cap and the normal channel noise is gone. I guess this cap was leaky and I don't have any DC voltage on those three pots anymore...
BUT the reverb still emits that noise/squeal/hum when I turn it past 3 on the knob. Do you think that could be a bad cap as well? Let me know your thoughts.
Thanks!
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No.. I'm not kidding.. I want all of this wire that you guys don't want.. 434 263-6189
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No.. I'm not kidding.. I want all of this wire that you guys don't want.. 434 263-6189
Well, help me solve my reverb and volume issues on this damn amp and I'll send you my wires! And they're coming to you from France, they're not scared of flying 6000 miles, let me tell you! :icon_biggrin:
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Yeah.. I DO have input on yer SR MALfuntion... you did something thoughtless ,( like we all do).
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Yeah.. I DO have input on yer SR MALfuntion... you did something thoughtless ,( like we all do).
Maybe I did, but so far the only reason why the normal channel wasn't working was not my fault but a bad cap's (thank you SOZO!!!) :icon_biggrin:
So, so far I'm still a good builder who was unlucky enough to receive a bad component. (And can caps be tested prior to installation btw and if so, with what/how?)
Oh, and I'll just add the stinky AES wires to the bad components list... Still want them worth? Come on, you can do better than this! :laugh:
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Look.. everyone here has gone through what ,you , have before you now. Have a drink.. or several take your time.. the problem WILL reveal itself.
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You've made a wiring mistake.
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I know worth, I was just kidding. I hope you didn't take offense. I was able to find the leaky cap, I guess I'll manage to find what is wrong with the reverb and overall volume. I'll just take any thoughts in the meantime...
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I'm 52 years old.. and I make amps all the time. I'm AMAZED at the stupid shit I do.. that usually reflects on the terrible crap that is going on in my life.
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I'm 52 years old.. and I make amps all the time. I'm AMAZED at the stupid shit I do.. that usually reflects on the terrible crap that is going on in my life.
When I said I'd take any thoughts in the meantime I meant thoughts about my build... :l2: (just kidding worth, just kidding...)
Damn, worth I'm 33... Does this mean that I will still have half of my amps non fully working at first start up in 20 more years??? :BangHead:
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I'm 52 years old.. and I make amps all the time. I'm AMAZED at the stupid shit I do.. that usually reflects on the terrible crap that is going on in my life.
Like posting your home phone # on line? :w2:
Take that down and send him a PM.
Brad :laugh:
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I never told you.. but your build is very pretty.. BUT you've got to stare at it, until YOUR mistake becomes obvious.
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I have got some WD-40, can I use it to clean the pot or not?
NO! :w2:
Glad you got some sound coming out now!
Brad :icon_biggrin:
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I never told you.. but your build is very pretty.. BUT you've got to stare at it, until YOUR mistake becomes obvious.
Thanks for the kind words. Absolutely. Or search and measure and search again until I find another bad component that ruins the great flawless work I did... :icon_biggrin:
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Hmm....shorted output jack? That's hard to fathom with switchcraft jacks.
Too much heat when you soldered that .1cap maybe?our work looks so neat,it's hard to see what you have done wrong.Too bad we are so far awy from each other,I'd come over and get it working for you!
Low volume issues can come from a lot of areas,so you built it,fix it bro!
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I'm signiing out.. my last word is.. you don't have a "bad" component.. WIRING MISTAKE !!!!! good luck.. really
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Hmm....shorted output jack? That's hard to fathom with switchcraft jacks.
Too much heat when you soldered that .1cap maybe?our work looks so neat,it's hard to see what you have done wrong.Too bad we are so far awy from each other,I'd come over and get it working for you!
Low volume issues can come from a lot of areas,so you built it,fix it bro!
Thx bro. I'm actually thinking about moving to Austin, TX, so I might be closer to you for my amp fixing issues. Music sucks over here. I'm in a blues/rock band and we can't even get to play because bar owners just have DJs and their crap come in and the police have bars shut down if they play too loud. And the rest of the venues are held on tight by professional musicians and heir friends who won't open their doors to new bands. You can't be a true musician in France anymore... Gotta leave this place behind and find a good music homeland and I've read that Austin is the place to be.
Well then I'll have to ask my wife and my two young boys if they'd be willing to move 7000 miles away. But the 4-year-old is already on the right track: when I listen to Joe Bonamassa in the car he says "Dad, I want Thin Lizzy"... My wife will kill me one day... :icon_biggrin:
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LAST UPDATE:
So I'm now concentrating on the vibrato channel and more particularly on the reverb pot. With all pots to 0 the reverb pot is silent. When I go past three on the reverb pot the amp starts emitting a hum that increases in volume even if I leave the pot on 3. So the amp hums even with the volume pot on 0... Bringing the volume pot up to 5 doesn't change a thing.
I stuck my MM on that pot to see if I have any DC leak and I don't have any. But the amp emits a noise when I touch the right and middle lugs...
I did the same thing trying to measure resistance and then I had a boom when I touched either lug...
I don't know what this means. This amp is exhausting.
I'm off to bed. Hope to read some advice or leads when I get up tomorrow.
Thanks!
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Mange la merde!
Damn Frenchies! They need a blues revival over there big time by the sounds of it. :l2:
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Hi.
After a good night's rest I finally found my only mistake on this build: I had installed a 470Ω instead of a 470KΩ in the reverb circuit... This caused the low volume output and interference with the volume pot... The main hum was due to the reverb cable which had slipped under the reverb tank while I shoved the tank in its bag. So I now have a fully working SR!
Anyway, I highly recommend the Weber DT10's in your SR builds. They have lower sensitivity and enable you to push the amp higher. On 6 it's good. And it won't kill the neighbours, if you don't add any pedal on top of that i.e.
And for once the reverb and tremolo are working as they should. Not too much, not too few. Perfect.
Just one thing regarding bias: I have a 451V B+ and =C= 6L6GC which dissipate 30 watts, so 70% of that is 23 watts. 23 / 451 gives 51mA... Ain't that a lot? I have them at 39mA and 34mA. Would you increase the current going to the tubes or leave as is?
Thanks guys!
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Just one thing regarding bias: I have a 451V B+ and =C= 6L6GC which dissipate 30 watts, so 70% of that is 23 watts. 23 / 451 gives 51mA... Ain't that a lot? I have them at 39mA and 34mA. Would you increase the current going to the tubes or leave as is?
Which type of tremolo do you have on the amp?
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The original tremolo... Optoisolator. Shown on pics...
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Try all bias settings and play the amp.Leave the bias where it sounds the best.51ma will get tube sellers in a frenzy cause they give warranty on tubes but I have run super's ate 45ma plus for years and have minimal tube failures.
Now a Marshall amp is another story.
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Sleepless, build yourself Dougs Listening Device. You will be able to pin point the trouble in minutes. All the info is on this site. Good luck to you. Punky
http://www.el34world.com/Hoffman/tools.htm (http://www.el34world.com/Hoffman/tools.htm)