Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on March 17, 2016, 05:40:10 pm
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Trying to improve my builds. Any opinions concerning the following would be greatly appreciated:
Placing IN4007 diodes between the HT lines from the PT and pins four and six of the rectifier tube socket. When looking for the best current production 5AR4 rectifier tube there were a lot of comments concerning failure rates with modern rectifier tubes. If a tube fails it can take out a PT at the same time which is a lot more expensive than two diodes. Seems like they could be installed using the unused pins on the rectifier tube.
Using a fuse on the high tap line like Marshall did. Not sure why they did it but there must be a reason.
Placing small value cap, either .01 or .1uF, across the power supply electrolytics. Wish I would have though ahead could have placed them on the power board and just wired them in.
Any suggestions concerning the above or other suggestions for improving a build would be very much appreciated.
Thanks
Mike
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Placing IN4007 diodes between the HT lines from the PT and pins four and six of the rectifier tube socket.
Good idea. Would probably have saved a bandmate's Sunn PT back in the '60s. I've never done it.
Using a fuse on the high tap line like Marshall did
Probably a good idea on bigger amps.
Placing small value cap, either .01 or .1uF, across the power supply electrolytics.
I don't see any value for this in an audio amp. In the days of high current TTL logic circuits, it was very common to have a .1 cap across the 5V/gnd supply pins of every IC. These caps acted as a small reservoir cap for each IC. They were commonly called despiking caps and prevented (or minimized) fast switching transients from running rampant across the +5v supply and coupling into other ICs.
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Placing small value cap, either .01 or .1uF, across the power supply electrolytics.
Vox do it on the AC30C2 - AC30CC2
http://el34world.com/charts/Schematics/files/Vox/Vox_AC30C2.pdf (http://)
http://el34world.com/charts/Schematics/files/Vox/Vox_AC30CC2_AC30CC2X%20(2005)%20SM.pdf (http://)
Why ? Bad e-cap to be "corrected" ?
Franco
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Placing small value cap, either .01 or .1uF, across the power supply electrolytics. Wish I would have though ahead could have placed them on the power board and just wired them in.
In a guitar amp I think it makes a good tonal difference on the last filter stage (feeding the 1st gain stage). Try an A/B test. Don't now if the difference would be noticeable in a live venue situation.
FWIW, attached are my usual PS mods.
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The protection diodes are cheap, and won't effect the functioning of the rectifier tube, and it only takes 2 mins to fit them - so you might as well do it.
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I put the diode backup on tube rectifiers. UF5408 diodes supposedly switch much faster and have less "switching noise" according to the AX84 crowd. Don't cost much more than standard 1N4007 diodes and are rated at 1,000 volts, etc.
http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1 (http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1)
There's debate about Mods 2-4. I don't know enough to have an opinion on the MOV resistors in front of the PT and OT. However, RG Keen knows what he's talking about in general.
Fusing seems to be reasonable.
http://el34world.com/Forum/index.php?topic=13538.0 (http://el34world.com/Forum/index.php?topic=13538.0)
Respectfully,
Chip
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Placing IN4007 diodes between the HT lines from the PT and pins four and six of the rectifier tube socket.
Good idea. Would probably have saved a bandmate's Sunn PT back in the '60s. I've never done it.
Using a fuse on the high tap line like Marshall did
Probably a good idea on bigger amps.
:hijack1:
What HT means?
How big an amp should be to have this fuse in this high tap line, is it B+ ?
Thanks
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HT means High Tension and refers to the PT secondary high voltage winding.
Marshall put a fuse in the B+ line of their Plexi 50. I have a 60 watt Sunn and a 80 watt Twin Reverb. Neither have a B+ fuse. I'd probably include a B+ fuse on any 50W project I build.
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HT means High Tension and refers to the PT secondary high voltage winding.
Marshall put a fuse in the B+ line of their Plexi 50. I have a 60 watt Sunn and a 80 watt Twin Reverb. Neither have a B+ fuse. I'd probably include a B+ fuse on any 50W project I build.
Cool, what this fuse is protecting?
Thanks
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I put the diode backup on tube rectifiers.
http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1 (http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1)
There's debate about Mods 2-4. I don't know enough to have an opinion on the MOV resistors in front of the PT and OT. However, RG Keen knows what he's talking about in general.
Fusing seems to be reasonable.
http://el34world.com/Forum/index.php?topic=13538.0 (http://el34world.com/Forum/index.php?topic=13538.0)
Respectfully,
Chip
I put the diode backup on tube rectifiers.
http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1 (http://www.premierguitar.com/articles/the-immortal-amplifier-mod-1)
There's debate about Mods 2-4. I don't know enough to have an opinion on the MOV resistors in front of the PT and OT. However, RG Keen knows what he's talking about in general.
Fusing seems to be reasonable.
http://el34world.com/Forum/index.php?topic=13538.0 (http://el34world.com/Forum/index.php?topic=13538.0)
Respectfully,
Chip
Thanks Chip, Those articles were great. Exactly what I was looking for. Seems like fuses one through four would be wise along with two IN4007 diodes feeding the plates of the rectifier tube. Was thinking about placing the diodes on the unused rectifier tube sockets but it looks like a board with room for two fuse holders and two diodes makes more sense. Will install a fuse on the HT line for any amp that is 50 watts or above as Sluckey suggested.
Thanks
Mike
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Placing small value cap, either .01 or .1uF, across the power supply electrolytics. Wish I would have though ahead could have placed them on the power board and just wired them in.
In a guitar amp I think it makes a good tonal difference on the last filter stage (feeding the 1st gain stage). Try an A/B test. Don't now if the difference would be noticeable in a live venue situation.
FWIW, attached are my usual PS mods.
That's a neat idea with the diode between R2 and C3, gotta remember that one. And of course, I'm curious about your chokes across the line coming in from the power plug?
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Placing small value cap, either .01 or .1uF, across the power supply electrolytics. Wish I would have though ahead could have placed them on the power board and just wired them in.
In a guitar amp I think it makes a good tonal difference on the last filter stage (feeding the 1st gain stage). Try an A/B test. Don't now if the difference would be noticeable in a live venue situation.
FWIW, attached are my usual PS mods.
Got a chance to download your attachment which is very much appreciated. Had some questions concerning same. First, curious how you arrived at the .1 versus .22 cap ratings across 10uF and 20uF caps respectively? Secondly, what is the advantage of placing the diode between the screen supply and preamp supply? Third, what size chokes do you use in the main AC supply and what do they do?
Thanks,
Mike
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May be I'm wrong but I interpreted the choke across the AC line as the indication of a line filter
(http://i00.i.aliimg.com/img/pb/473/843/614/614843473_804.jpg)
I consider good practice to have one of those filters at the input of the AC line in the chassis
Franco
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ah, now I see! Thanks!
advantage of placing the diode between the screen supply and preamp supply?
I'm probably wrong, but I looked at it as taking out more ripple?
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The purpose of that diode is to avoid the discharge of the electrolytic capacitor/capacitors that feeds the preamp tubes when the power tubes drain their electrolytic capacitor/capacitors during peaks
Franco
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advantage of placing the diode between the screen supply and preamp supply?
I'm probably wrong, but I looked at it as taking out more ripple?
That diode provides isolation between the low current downstream nodes and the high current plate/screen nodes. The effect is that nodes c and d will not sag or be pulled down due to current fluctuations in the power amp. For example, let's say that node c voltage is 350V. Maybe a strong power chord causes the upstream nodes a and b to momentarily dip below 350. That diode becomes reverse biased and prevents juice from draining out of the node c and d caps. So the downstream nodes are unaffected by load demands put on the power amp nodes.
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The AC choke is to reduce AC power line noise. Nothing fancy. Just snap on over the power chord, from Radio Shack. More elaborate units could be used.
The diode in the PS is an idea from Dan Torres. It "rectifies" the preamp in his words. It preserves transient spikes in signal. A transient spike in the power amp section increases current draw. The diode forces the current draw to come from the wall outlet, not from the preamp.
The small cap should be about 1/100 the value of the main filter cap
Try different bypass cap values to see if it sweetens the amp's tone.
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May be I'm wrong but I interpreted the choke across the AC line as the indication of a line filter
(http://i00.i.aliimg.com/img/pb/473/843/614/614843473_804.jpg)
I consider good practice to have one of those filters at the input of the AC line in the chassis
Franco
Thanks Franco, this makes good sense to me. Looked up the AC EMI Filter and noticed it comes in 1A, 3A, 6A and 10A sizes. Wouldn't it make sense to order the 10A size if you have an AC fuse behind it? That way you wouldn't have to be concerned with it malfunctioning.
Thanks,
Mike
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Thanks Franco, this makes good sense to me. Looked up the AC EMI Filter and noticed it comes in 1A, 3A, 6A and 10A sizes. Wouldn't it make sense to order the 10A size if you have an AC fuse behind it? That way you wouldn't have to be concerned with it malfunctioning.
If physical size and cost are not a factor.
You could also use 10 watt resistors throughout an amp. :icon_biggrin:
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advantage of placing the diode between the screen supply and preamp supply?
I'm probably wrong, but I looked at it as taking out more ripple?
That diode provides isolation between the low current downstream nodes and the high current plate/screen nodes. The effect is that nodes c and d will not sag or be pulled down due to current fluctuations in the power amp. For example, let's say that node c voltage is 350V. Maybe a strong power chord causes the upstream nodes a and b to momentarily dip below 350. That diode becomes reverse biased and prevents juice from draining out of the node c and d caps. So the downstream nodes are unaffected by load demands put on the power amp nodes.
Thanks Sluckey, any idea how preventing juice from draining out of nodes c and d would impact the amps tone. I guess what I am asking is does tube amp sag come from the power tubes, preamp tubes or both. Some amps you want sag in and some you don't. This is definitely an inexpensive mod, certainly no reason not to test it to see if you like it.
Thanks,
Mike
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Thanks Franco, this makes good sense to me. Looked up the AC EMI Filter and noticed it comes in 1A, 3A, 6A and 10A sizes. Wouldn't it make sense to order the 10A size if you have an AC fuse behind it? That way you wouldn't have to be concerned with it malfunctioning.
If physical size and cost are not a factor.
You could also use 10 watt resistors throughout an amp. :icon_biggrin:
Not sure about the cost because the Mouser site is down but the size is the same regardless of current. I put three watt precision metal film resistors on the plates and across the cathode bypass caps to reduce hiss now and in the future. Definitely overkill on what is required but three years from now there shouldn't be intermittent static or increased hiss because the resistor dried out and cracked because it was near its limits.
Thanks,
Mike
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Thanks Franco, this makes good sense to me. Looked up the AC EMI Filter and noticed it comes in 1A, 3A, 6A and 10A sizes. Wouldn't it make sense to order the 10A size if you have an AC fuse behind it?
I think you want to order the filter entry module with the current rating closest (but above) what your circuit will draw. The L & C values in the line filter give the designed noise attenuation at the rated current draw. So if you have a 3A amp, you want a 3A line filter.
Jon
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... does tube amp sag come from the power tubes, preamp tubes or both. Some amps you want sag in and some you don't. ...
Sag usually is an audible artifact in the power amp portion of your amplifier.
The output tube plates pull the most current of the entire amp, followed by the output tube screens. The biggest current spikes for each happen when the amp is being played very loudly, during the brief peaks in the signal. If the current peaks exceed the power supply's ability to deliver current (for whatever reason, but often due to series resistance, perhaps in the form of rectifier voltage drop and/or small filter capacitance), the supply voltage drops, which tends to also result in reduced current draw, and so total power is momentarily reduced over what it would be if voltage did not sag.
The big obvious way to add sag is to increase the series resistance between the power transformer and the output tube plates. That might take the form of a higher-voltage drop rectifier (5R4 or 5Y3 instead of a 5AR4/GZ34 or solid-state). It might be added series resistance between the rectifier and a filter cap feeding output tube plates. It could be higher winding resistance of the power transformer itself. Or in some old tube circuits, it might be a resistor between each side of the PT high voltage winding & the rectifier plates.
A second way to induce sag is to increase series resistance leading to the output tube screen. The output tube needs a solid screen voltage to make the most output power, because the screen voltage impacts potential plate current more than the plate voltage. So if screen voltage drops, maximum possible plate voltage drops, too. This is why old amp manufacturers might use a series resistor in the power supply for their small amps, but often use a choke leading to the screen's filter cap in their bigger amps. They're trying to reduce the possibility of dropping screen voltage to reduce sag and get the most power output.
Which also explains why the same manufacturers originally might have no series screen resistor (it could cause screen voltage to drop right at the moment the plate current is trying to reach its peak, thus reducing power output). But a screen resistor also insures that excessive screen current (perhaps in a fault condition or just with very large input signals) won't cause the screen to overheat and/or melt. So manufacturers typically use the smallest resistor they can (470Ω or at most 1kΩ) to limit screen dissipation while also minimizing impact to screen voltage.
You can purposely do the opposite: raise screen resistance to induce screen voltage drop, raise sag and limit output power. The value to use depends on your needs for maximum volume and desired sag. You might experiment with 2-4kΩ screen resistors, see what you think & raise/lower to taste.
Where the output tube plates draw 10's of mA at idle up to maybe 100's of mA at peak output, and output tube screens draw a few mA's at idle up to 10's of mA at peak output, the preamp tubes may only draw a part-mA at idle up to maybe 1mA at peak output. These low currents aren't likely to drain even small filter caps appreciably, and if you raise the plate load resistor to impact plate voltage directly, you change the operation of the tube drastically. So it's less practical to induce sag in the preamp (apart from some clever plans of causing compression by controlling a preamp pentode's screen with a large, later-stage signal, rectified into a control voltage).
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> AC EMI Filter and noticed it comes in 1A, 3A, 6A and 10A sizes. Wouldn't it make sense to order the 10A
The right-size unit will filter better (or cost/size less).
I can't, offhand, think of ANY tube amplifier would need a 10 amp feed. My Bogen stack wasn't far over 6A at 117V.
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May be I'm wrong but I interpreted the choke across the AC line as the indication of a line filter
(http://i00.i.aliimg.com/img/pb/473/843/614/614843473_804.jpg)
I consider good practice to have one of those filters at the input of the AC line in the chassis
Franco
I can't see any US distributors for the EMI line filters. Any suggestions.
Thanks,
Mike
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This ?
http://www.ebay.com/itm/FN9222-12-06-SCHAFFNER-AC-POWER-ENTRY-MODULE-12A-FILTER-PERFORMANCE-/351550956720 (http://www.ebay.com/itm/FN9222-12-06-SCHAFFNER-AC-POWER-ENTRY-MODULE-12A-FILTER-PERFORMANCE-/351550956720)
http://www.ebay.com/itm/223-10-06-SCHAFFNER-AC-POWER-LINE-FILTER-MODULE-10A-/351576618325 (http://www.ebay.com/itm/223-10-06-SCHAFFNER-AC-POWER-LINE-FILTER-MODULE-10A-/351576618325)
Franco
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These are the snap-on power line line filters I've used: http://www.ebay.com/itm/like/121663772868?lpid=82&chn=ps&ul_noapp=true (http://www.ebay.com/itm/like/121663772868?lpid=82&chn=ps&ul_noapp=true)
But I really like the ones posted by Kagliostro.
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This ?
http://www.ebay.com/itm/FN9222-12-06-SCHAFFNER-AC-POWER-ENTRY-MODULE-12A-FILTER-PERFORMANCE-/351550956720 (http://www.ebay.com/itm/FN9222-12-06-SCHAFFNER-AC-POWER-ENTRY-MODULE-12A-FILTER-PERFORMANCE-/351550956720)
http://www.ebay.com/itm/223-10-06-SCHAFFNER-AC-POWER-LINE-FILTER-MODULE-10A-/351576618325 (http://www.ebay.com/itm/223-10-06-SCHAFFNER-AC-POWER-LINE-FILTER-MODULE-10A-/351576618325)
Franco
Even better 12 whole amps of EMI protection. Thanks Franco.
Thanks
Mike
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These are the snap-on power line line filters I've used: http://www.ebay.com/itm/like/121663772868?lpid=82&chn=ps&ul_noapp=true (http://www.ebay.com/itm/like/121663772868?lpid=82&chn=ps&ul_noapp=true)
But I really like the ones posted by Kagliostro.
Thanks for the reply John. There was a recent thread on using the ferrite beads for EMI reduction. Never heard of it before reading the thread. As a side note the last Radio Shack in our area went out of business today. Can't say I bought a lot from them but it is sad to see the end of an era. Would buy all the Radio Shack parts you think you can use now. Don't think they will be available for much longer. Will need sites like Hoffman's even more now.
Thanks,
Mike
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I don't know the USA market, but here (Italy) is not difficult to recover the filter I posted in old LCD TV and other dismissed apparatus
in old UPS you can find this type of filter
(http://www.newark.com/productimages/standard/en_US/4628992.jpg)
Franco
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... does tube amp sag come from the power tubes, preamp tubes or both. Some amps you want sag in and some you don't. ...
Sag usually is an audible artifact in the power amp portion of your amplifier...
HBP, thank you so much for the well thought out and written response. Pretty sure I understood every word of it which makes this a good day.
Thanks,
Mike
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Looking at one of the EMI parts Franco posted I noticed there appears to be four caps, a resistor and two .1mH chokes in it. To my way of thinking it would be advantageous to reduce EMI interference coming into the amp through the AC line.
I have two objectives. One is to make an amp that sounds good. I think the part could only help in that regard. Secondly, I want it to last a long time. Any idea whether there is a likelihood of premature failure? Less than 20 years is a premature failure for purposes of this discussion. This is a 12A part used in a 1A amp. May use it in an amp that has a five amp fuse.
Thanks,
Mike
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May be someone told this previously on this thread but I don't remember
one GREAT improve for long time life is to avoid the use of ecaps and use poly
the counterpart is they are very BIG and expensive
see the filter caps on HotBluePlates 25L15 Standel inspired amp
(http://el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=31258;image)
Franco
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I normally get EMI filters from old computer power supplies. Most of the ones I have removed have the info right on them and are 6 amp. Lately I have been seeing some with fuses, but have not pulled any. Normally I have plenty of room for them, but I do install them vertical in amps.
I believe diode protection to be a no brainier and ANY amp with a tube rectifier I add them even if I am just changing tubes and rebias. I do put them inline with the HT leads where if the tube dies the amp will quit. Just my preference as I usually run my tubes pretty hot and the additional voltage from a 5Y3 to SS rectification will red plate if running at 70% unless your bias follows.
I use circuit breakers on B+ and and AC on amp builds. I use the flat buss fuse holders on vintage amps. I add those to my personal amps, even collectible ones as it is easy to remove since most amps have a convenient place to screw them down. For point builds I like the inline twist like the Littlefuse 155.
Actually on a current build I am using a lot of diodes like you see in Ken Fisher's work.
Very cheap insurance and it is something that if another tech down the road see they should immediately know why they are installed.
I have an old Valco amp that had a light bulb, automotive 1156 bulb, across the field coil speaker. I did not get that one and after checking I found it not to be original so I removed it. Never found out why anyone would do that, but I guess whoever did it was attempting to save the speaker.
I have some old PA Mains, Audio Centron that uses this same bulb to protect the horns and seem to work well.
I do not know if anyone mentioned this already, but I like to use a 5 Watt, resistor across the output jack of my smaller watt builds to help protect the OT in-case someone forgets to plug in a cabinet.
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May be someone told this previously on this thread but I don't remember
one GREAT improve for long time life is to avoid the use of ecaps and use poly
the counterpart is they are very BIG and expensive
see the filter caps on HotBluePlates 25L15 Standel inspired amp
(http://el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=31258;image)
Franco
I really like these caps and for me they are worth every penny. Now in 20 more years I probably will not pay the difference because then cheaper caps like Illinois will not outlive me. :laugh:
BTW, Nice work. Very neat.
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May be someone told this previously on this thread but I don't remember
one GREAT improve for long time life is to avoid the use of ecaps and use poly
the counterpart is they are very BIG and expensive
see the filter caps on HotBluePlates 25L15 Standel inspired amp
(http://el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=31258;image)
Franco
Thanks Franco, I used one of the 20uF Solen Fast Caps in my current build to feed the preamp section. Bought four of them years ago for a 5F6A build. Needless to say they didn't fit under the cap can so didn't get used. They are huge.
Thanks,
Mike
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..... automotive 1156 bulb, across the field coil speaker ....
A field coil is like a choke ..... a bulb is a .... variable resistor (changes resistence from cold to hot) ........
(http://i.imgur.com/EG7oEV0.gif) (http://i.imgur.com/EG7oEV0.gif) (http://i.imgur.com/EG7oEV0.gif) :w2: :w2: :w2:
here you can see something similar, but not the same
http://el34world.com/Forum/index.php?topic=14404.msg136368#msg136368 (http://el34world.com/Forum/index.php?topic=14404.msg136368#msg136368)
(http://i.imgur.com/utFtgTN.jpg)
Franco
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You can purposely do the opposite: raise screen resistance to induce screen voltage drop, raise sag and limit output power. The value to use depends on your needs for maximum volume and desired sag. You might experiment with 2-4kΩ screen resistors, see what you think & raise/lower to taste.
Of all the things HBP has posted and the help he has provided, this one is my favorite. Not only can it give sag to an amp if you desire, I have also used it to benefit Marshall EL34 topology by removing some brittleness. I have used a lot of different values and even made the values switchable. On the Marshall, I have settled on 3K3 as my preference. My gigging Super Reverb has resistors on a rotary switch, 3 values. Stock, 1k5 and 2k7.
At normal playing levels, not cranking, which on a SR is usually between 3 and 4 on the knob switching to the 2k7 gives almost the exact feel when it is cranked. I say almost because the speakers are loafing.
Great topic!!!
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Had another thought. When I was building my three Dumble clones I was always curious if his covering the circuit board in opaque gunk was solely due to his paranoia about anyone stealing his ideas or maybe also had to do with tone and reliability. Read recently that movement, even slight movement, in AC lines can inject hum into an amp. Suggested solid core wire for heaters to reduce wire movement. I do know that solid core wire for heaters running over the sockets is risky. Doesn't take much wire movement when tinkering around the socket to break the wire making that tube and any other going to V1 inoperable.
Question I had is do you think it is advantageous to make components so they can not vibrate? If so, how would you do it?
Thanks,
Mike
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I think Dumble gunked it to prevent casual copying. Yes, it is good engineering practice to prevent things from moving. Solder joints can break from continuous strain or severe vibration over time. That said, I don't glue down/RTV electrolytic caps, and only occasionally lace/tie cables inside my builds. I'd say the main breakage hazard for wire connections is caused by nicking the wire/strands when stripping the insulation. Copper wire also exhibits work hardness, i.e. becomes brittle from repeated bending.
The classic standard for good guitar amp construction is Hiwatt amps assembled by Harry Joyce and crew. I don't know how much more benefit there is to be gained by going beyond that.
Conformal coatings are standard when the equipment is subject to severe environments like salt spray (marine/naval), or aircraft/vehicle applications. For "normal" applications it just makes maintenance/tweaks/mods more difficult. Other weak points in amps are the quality of jacks, tube sockets, and tube retainers. You could also use military variants of all the tubes, with triple mica spacers and stronger support structures. Some tube types are more microphonic than others, and will sing no matter how much you tie everything else down.
You can copy the construction practices from classic Tektronix and HP test equipment. HiFi is full of cultists bent on damping vibrations and resonances from all the electronics.
I think 99% of reliability and tone comes from making good mechanical connections with wire and components, proper soldering technique, proper layout, and using good (not exotic) parts.
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I think 99% of reliability and tone comes from making good mechanical connections with wire and components, proper soldering technique, proper layout, and using good (not exotic) parts.
Me too.
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I think 99% of reliability and tone comes from making good mechanical connections with wire and components, proper soldering technique, proper layout, and using good (not exotic) parts.
Me too.
That was a very good answer. Just threw out the part vibration out of curiosity. Like the response from vibrolax. Makes a lot of sense.
Thanks,
Mike
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Your car leads a physically rougher life than your amp. (Especially when the frost comes out of the Maine pot-holes.)
Car wires are not "gooped".
Bill Creller (http://el34world.com/Forum/index.php?topic=16817.0) is an airplane fixer, including some very old airplanes. While airplanes hit fewer pot-holes, some fly a LOOONG time (see his 1947), vibrating all the way. I don't think they are gooped. True, they ARE inspected on-schedule, and owners can't complain if repairs are necessary. (Well, they complain, but if a plane is not air-worthy the pilot who flies it is in deep trouble.)
I vote for keeping it accessible for look-over and repair. (Wish Honda thought about wire inspection; I've had every piece of the dash out and still don't know why the radio and clock go out. They must prop up the wire-harnesses then build the car around them.)
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This standard is dismissed but still a valid way to do things
http://www.hq.nasa.gov/office/codeq/doctree/canceled/NS87393-Ch5.pdf (http://)
http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/613%20Terminals.html (http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/613%20Terminals.html)
http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/601%20General%20Requirements.html (http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/601%20General%20Requirements.html)
Other good stuff
! No longer available (http://www.youtube.com/watch?v=vIT4ra6Mo0s#)
Here the whole collection of video
http://www.stevenjohnson.com/soldering/instruction.htm (http://www.stevenjohnson.com/soldering/instruction.htm)
Give them a look and also if you remember only few things is all gained
Franco
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This standard is dismissed but still a valid way to do things
http://www.hq.nasa.gov/office/codeq/doctree/canceled/NS87393-Ch5.pdf (http://)
http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/613%20Terminals.html (http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/613%20Terminals.html)
http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/601%20General%20Requirements.html (http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/601%20General%20Requirements.html)
Other good stuff
! No longer available (http://www.youtube.com/watch?v=vIT4ra6Mo0s#)
Here the whole collection of video
http://www.stevenjohnson.com/soldering/instruction.htm (http://www.stevenjohnson.com/soldering/instruction.htm)
Give them a look and also if you remember only few things is all gained
Franco
Thanks Franco, great post. According to the NASA specs any hookup wire we would use in our amps (usually 20 or 22 gauge) should be wrapped a minimum of 1/2 turn (180°), to a maximum of 3/4 turn (270°) around the turret as close as possible to its base. Guess this makes sense because if the wire is tightly wrapped around the turret there is stress on the wire. Relieving that tension could place strain on the solder joint. Also, should not solder components to the holes on top of the turrets unless the component is flush to the circuit board. Makes sense because the weight of the component would cause stress on the solder joint. That would work easier for axial components versus radial components. Additionally, when running a wire from turret to turret, as would be done for grounds or tying the resistors in the PI circuit together for instance, the wire can be wrapped around the turret. However, there should be stress relief (in other words you need to leave a little slack and don't pull the wire too tight) in the wire between turrets. This makes sense because if there is a lot of tension from pulling the wire too tight it would place stress on the solder joint. Other great information on wiring to anything with a hole in it. Exposed stripped wire should be less than twice the thickness of the wire between the insulated wire and the turret.
Looked at my current build. Wrapped wires at least all the way around turret thinking it would be more secure. When wiring more than one turret with the same wire didn't leave any stress relief. Again thinking a tight wire would be more secure. Just about all the resistors and caps on the circuit board are soldered to the tops of the turrets and are floating in the air. Any suggestions? Help! Sometimes it is so much easier to be ignorant. However, if you want a top-notch build you must build a top-notch build.
Thanks,
Mike.
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I vote for keeping it accessible for look-over and repair.
Thanks PRR, accessibility for repair is definitely the big argument for no goop.
Thanks,
Mike
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At the risk of repetition, here are Doug Hoffman's videos on how to lace up turret connections:
https://youtu.be/VAekembI9-s?list=PLVvDFekIYJjflOUPVAV9ENuznt6IgBF4_ (https://youtu.be/VAekembI9-s?list=PLVvDFekIYJjflOUPVAV9ENuznt6IgBF4_)
If you scroll down a ways here, you'll see Doug's method for installing components:
http://el34world.com/charts/toolhowto.htm (http://el34world.com/charts/toolhowto.htm)
This page is packed with useful info though, including the first two links above:
http://el34world.com/Hoffman/instructions.htm (http://el34world.com/Hoffman/instructions.htm)
Ah, here are the "board building instructions" from the Library:
http://el34world.com/boardmaker/BOARD0.htm (http://el34world.com/boardmaker/BOARD0.htm)
Yes, there is a lot of overlap between these links. However, I think you'll find that there are useful bits in some which aren't covered in others. Besides, reading this stuff repeatedly helps me remember...
Respectfully,
Chip
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HT means High Tension and refers to the PT secondary high voltage winding.
Marshall put a fuse in the B+ line of their Plexi 50. I have a 60 watt Sunn and a 80 watt Twin Reverb. Neither have a B+ fuse. I'd probably include a B+ fuse on any 50W project I build.
Cool, what this fuse is protecting?
Thanks
This HT fuse protects the transformers if there is a short between the B+ supply and the ground return (which could otherwise cause an excessive amount of current to be drawn through the PT, or if the short is in one of the output tubes - through the primary winding of the OT.)
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On Fixed Bias amp you can place a fuse between ground and cathode of the power tubes
like in Fender Bassman 300W
(was told previously ?)
Franco
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Purchase four EMI power modules on ebay for $2.00 each figuring what can it hurt. Noticed a problem as soon as they arrived. Have a C16 receptacle not the C14 receptacle common to musical equipment. AC cords can be purchased to fit them but I find it inadvisable to create an amp that needs a special cord.
Reason for this fiasco is these are 12 amp modules. Convinced, right or wrong, that a bigger module would be less likely to have problems when I bought them. Looked on Mouser and noticed the 12A module has .11mH chokes whereas the 3A module has 2.5mH chokes. In fact the larger the amperage the lower the mH rating for these products. Would it be better to have bigger chokes on the line? If so, I can throw the modules I received today in the garbage and buy 3A or 6A modules from Mouser.
Thanks,
Mike
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... Reason for this fiasco is these are 12 amp modules. ... and noticed the 12A module has .11mH chokes whereas the 3A module has 2.5mH chokes. In fact the larger the amperage the lower the mH rating for these products. Would it be better to have bigger chokes on the line? ...
How much current does the amplifier draw? Probably 3A or less, right? It seems silly then to try to acquire the higher-amperage models.
I didn't know the cords would be different, but it makes sense if you think about the fact you're going from typical "consumer-size" to a current rating similar to the wiring in your wall.
Assume the people designing those power entry modules know a bit more about the design of their product than you do. I'm sure that whatever value chokes and caps they use will be appropriate to the task. In all likelihood, the values of those parts are scaled to each other, and probably to the line frequency. There's likely a number of other tradeoffs as well.
Reason for this fiasco is these are 12 amp modules. Convinced, right or wrong, that a bigger module would be less likely to have problems when I bought them. ...
Would using 10 gauge wire through the amp in place of hookup wire make it any better? Probably wouldn't be as easy to work with...
I went through a period of this same thought process when I started amp tinkering. "It's gotta be better to use 1w resistors in place of 1/2w, right? If 1w is good, 3w is better, right? What about those 25w aluminum-clad resistor for cathode bias?" Over time, I learned it's cheaper to use just-good-enough parts, and in some places you want the $0.50 resistor to burn up and fail rather than the $150 output transformer.
So Right-Sizing is often better (and cheaper) than over-spec.
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This would be the cheap option if not for the fact that I won't use them. Mouser wants almost $8.00 for the 3A part. This 12A part was $2.00. The 12A part is commonly used for equipment with heating elements in them. It has a notch in the receptacle so a heavy gauge power cord must be used. Makes all the sense in the world but doesn't work for a guitar amp. Take the amp to a gig and forget the cord and your out of luck. Not out enough money to worry about. Would cost as much to return it as I would get back. Live and learn if this is the most expensive lesson for the year this will be a good year.
Thanks,
Mike
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This would be the cheap option ... almost $8.00 for the 3A part. This 12A part was $2.00. ...
I just found out the same thing buying parts for a 1/3w amp. Was looking for a 1w resistor (maybe even a 1/2w would have worked), but the same thing in 3w was cheaper. Guess it's a higher selling-volume part...
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Diodes to protect OT and Power Tubes was told previously ?
Franco
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Good soldering techniques.
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Here are some things I have done with my amps and not mentioned in this thread so far:
Fast acting fuse (inside EMI power entry module)on the primary of PT, rated just above the max current for transformer :w2:
Inrush current limiter on the primary of PT (for my amp I used CL90 wich has 120 ohms cold, but goes down to 3 ohms at 1A) :laugh: fast acting fuse does not blow....
Thermal cutoff on the primary of PT, rated 100oC
Every single tube heater wired with separate twisted pair( no daisy chain)that way current through them is much smaller, and EMF they create is also smaller.
Designated cathode resistor (and capacitor) for each output tube in PP configuration.