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Dirty-South Blues Harp forum: wail on! >
How did you guys learn to build/tweak tube amp ?
How did you guys learn to build/tweak tube amp ?
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silpakorn
73 posts
Jun 29, 2011
7:43 PM
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...and where can I find the good source on the internet ? I'm just can't get the idea out of my head now and so desperately wanna understand what are they talking about when the conversations about amps moving into electronicians/amp tweakers area. Yeah, I'm a beginner who have a tendency to become a gearhead and should rather spend time practicing than talking about gear : ) actually, it's more like a very long term plan ( a year or two.. ) that I figured I better start studying it now little by little so I'll be able to build one when I'm ready in the future. I just love everything about it, I love tube amps for my stereos at home before I got into harps and it always a part of my plans to learn some woodwork ( I have a carpenter friend ) and a nice-retro tube amp is the thing that combined it together. I've been looking around for books, dvds, kits and instructions on the internet but not sure where would be a good place to start.. a book from torresengineering.com ? A Gerald Weber's dvd ? and where would be the best place for kits and instructions ? Any thoughts, comments is appreciated. Thanks.
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Joe_L
1322 posts
Jun 29, 2011
7:52 PM
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I took a high school electronics class and developed a healthy respect for electricity. As a teenager, I build some Radio Shack kits and learned how to solder. I learned how to use a multi-meter then.
A few years ago, I build a 5F1 Champ kit that I bought from Marsh Amps. It came with instructions. I went slow and followed the layout. It was pretty easy. The most difficult part for me was determining how to ground the amp. I had a problem. I enlisted a more knowledgeable friend for assistance.
It was a fun experience. It's a great sounding amp.
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silpakorn
74 posts
Jun 29, 2011
8:17 PM
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From what I've seached it seems like if you wanna get a kit with a very detailed instruction you better go to guitar amp sites but the problem is I can't tell which one would be a good choice since they are not voiced for harp. Any suggestions 5F1, 5E3...?
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markdc70
81 posts
Jun 29, 2011
8:52 PM
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Fat Dog Amps is selling their amps as kits now also.
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5F6H
757 posts
Jun 30, 2011
1:58 AM
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Gerald Weber's books are very useful as they are aimed at practical mods & servicing (rather than endless math on stuff like transformer design, which you don't need to know yet), "A desktop guide to hip tube amps" covers much of the basics & has a glossary at the end of chapters. "All About Tube Guitar Amplifiers" (also by Weber) would also be a good choice.
The Torres book is a very basic start if you know nothing, but ultimately of limited value.
A 5F1 would be a better choice to my mind than the 5E3, simply because there are quirks in the 5E3 design & layout that can cause pitfalls to a novice builder. The 5F1 circuit is about as simple as amps get & should be quicker & easier to trouble shoot if you have any issues (there is also a step by step photo build at www.tubeampdoctor.com). 5F1 is also easily "voiced for harp" should that be deemed necessary...bear in mind there is no common consensus on what exactly "voiced for harp" means. An amp voiced for harp may be a one off design, or a reproduction of an existing amp that happens to work well for harp...or be anywhere between those points.
Bigger amps just have more 12A#7 stages hooked up before the power section & the power section tends to be "push-pull" (power supply feeds the middle or "centre tap" of the OT with a tube at both ends) for amps over 10W, rather than "single ended" like the champ (power supply is fed in at one end of the OT, a tube is at the other end).
Also consider carrying out some simple mods to larger amps, like servicing & rebiasing, it helps you gain an understanding of each section, as it can take a while to see the big picture & how everything interacts.
Books are good up to a point but you really have to get your hands dirty to learn anything. A lot of kits also copy quirks & idiosyncrasies of old amps, so there are often little tricks you can apply to builds to reduce problems later. You are always welcome to drop me a PM. Oh, and familiarise yourself thoroughly with "ohm's law".
Here's a bit I wrote on another forum..
First you need to learn to drain hi voltage from an amp that is unplugged from the wall, some amps have bleeder resistors to do this, but don't guess - whenever I have an chassis out of an amp, or with the circuit exposed, I clip a jumper wire from a chassis ground point to the "plate/anode" pin of a 12A#7/5751 type tube socket (pin 1 or 6 ...check pinout for other preamp tube types), this bleeds the caps via the power supply resistors in around 30 seconds. As long as you can see the jumper in place you know you are protected, disconnect jumper before powering up again.
Never put your fingers in an amp that is connected to wall AC, similarly leaning on a chassis like BF/SF Fender that is plugged into the wall can give you a jolt from the power switch. Only ever probe with one hand, you don't want your chest/heart between the voltage entry & exit points should a shock go through your body. Buy a decent DMM with clips/wire grabbers, make all connections with the amp unplugged from the wall, power up take your readings, power down then move any meter leads to take the next reading, labour intensive but safest until you are familiar with probing circuits.
As with anything, if you break down schems, bit by bit, they are easier to figure. Generally tubes have 3 components - a grid, a plate, a cathode.
Signal goes in on the grid (which will have a load resistor to ground), then comes out on the plate (which is connected to the high dc voltage by a "plate resistor" of 56K to 220K, usually 100K), then goes through a coupling cap (this lets AC signal pass but keeps dc off the next tube's grid, as this would screw up the bias) to the next stage/volume control/tone stack. The 3rd tube component is the cathode, usually just has a resistor to ground that "biases" the tube (this resistor may be bypassed by a cap to increase gain), setting the idle current, all current that passes through the tube must leave via the cathode so sometimes signal is taken from here too, such as in a "cathode follower" tonestack (see V2 in a tweed bassman) or a "cathodyne phase inverter" (see 5E3 deluxe, 12AX7 next to the power tubes).
Power tubes usually have a 4th component, the "screen grid" which is connected to the high voltage supply via a resistor of 470ohms to 1kohm for 6V6/6L6/EL34/6550/KT88/KT90, or 100ohms+ for EL84. Sometimes power tubes are "cathode biased", as above via a resistor, or more often "fixed bias" by grounding the cathode directly & applying a negative voltage to the grid to bias the tube. Power tube plates are normally connected to the output transformer primary winding, rather than a plate resistor, for their dc supply.
Rectifiers just have plates & cathodes, AC applied to the plates comes out as dc on the cathode & feeds the amp's power supply, or diodes are used instead.
Tubes all need a low voltage, high current "heater/filament" supply to work...these only need investigating if they go wrong.
2 types of electricity are primarily at work:
AC signal - starts at the mic, goes from the input jack to, preamp tubes, power tubes, output transformer, then the speaker & carries the sound of your harp. This is what your amp's power rating is, measured in, AC W RMS.
dc B+ voltage - starts at the power transformer, via the rectifier, power tubes to the preamp tubes (opposite way to the AC). Tubes need the dc to operate. dc W ratings relate to how much heat resistors & tubes can take before they die.
Even little tiny tube amps carry potentially lethal voltages, so google & always follow appropriate safety procedures.
...now you know everything that I know...
Last Edited by on Jun 30, 2011 3:45 AM
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silpakorn
75 posts
Jun 30, 2011
6:05 AM
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@markdc70, it was the Fat Dog kits that got me interested in this idea but right now their products are not available because they're changing builder. I hope they'll come back soon though..
@5F6H, well, I have to admit that your name was the first one that came to mind when I decided to post this : ) but your comment is even more than I expected. I really appreciate it, seriously, come to Bangkok someday and I'll buy you a lot of beers !
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chromaticblues
898 posts
Jun 30, 2011
6:46 AM
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@silpakorn
If your interested I have A number of books on the subject that I don't need anymore. Some of these books you will never be able to buy again! I'll sell them all for $100. I would say I have around 10.
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walterharp
633 posts
Jun 30, 2011
6:57 AM
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i used a weber kit and liked it. problem with them is that they do not come with cabinets anymore, so you have to find a source for those...unless you are a good wood worker.
probably the biggest skill you need to learn is how to solder well. It is not a trivial skill and the performance (if it works at all) and durability of what you build can heavily depend on this.
During your build if you have problems, there is a friendly harp amp building forum at lone wolf blues, and the weber amp forms are also useful. the lone wolf forum will also suggest harp friendly changes to the schematic that you can incorporate as you build, rather than going back in and changing later.
If you are not sure of things, you can have an amp tech check your build when you are done, before you plug it in, to check things over and help with biasing etc.
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bluzmn
33 posts
Jun 30, 2011
8:53 AM
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As someone who is still learning himself, I have some suggestions:
In addition to the books already mentioned, there's "Dave Funk's Tube Amp Workbook": "How To Service Your Own Tube Amp" by Tom Mitchell: "The Tube Amp Book" by Aspen Pittman: and right now I'm reading the "RCA Receiving Tube Manual" which is a kind of a hard read, with a lot of math, but it gives you some insight into where some of those original circuit designs came from.
There's also the "Electric Guitar Amplifier Handbook" by Jack Darr which people "in the know" say is the best book ever written about amp repair; you can Google it and download it online. In addition to the forums already mentioned, there's music-electronics-forum.com, which has a separate forum about harp amps; Bruce Collins, who designed the 5f2h for Weber, often participates.
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silpakorn
76 posts
Jun 30, 2011
9:24 AM
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@chromaticblues, I've sent you a mail.
@walterharp, I've just started to learn how to make a finger joint today with my carpenter friend !
@bluzmn, thanks for the advice, those books are interesting especially the last one that I can get it online.
I'm really glad I asked, you guys are generous !
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Joe_L
1323 posts
Jun 30, 2011
9:50 AM
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When I decided to build an amp, I picked the 5F1 for the following reasons.
1. I was looking for an amp to play at home. The 5F1 was the smallest amp kit available. (I didn't realize that 5 watts would be quite loud in the house.) I owned a Pro Junior at the time. I liked that amp a lot, but it was way too loud for playing in the house.
2. I wanted a physically small amp and something that was generally considered a good sounding harp amp. I referenced David Barrett's web site. He wrote this about the 5F1, "Great big sound... itty bitty package... Very crunchy and bright from class A circuit, single knob control and 8" speaker!"
3. There were a lot of source for 5F1 kits. At the time I purchased my amp, Weber was experiencing problems with sourcing of cabinets. I didn't want to build a cabinet.
4. I had a (harp player) buddy that had an original 5E3 tweed deluxe. He seemed to be constantly fighting feedback at low volume levels.
5. The 5F2H from Weber wasn't available yet. It became available about a week or two after I placed my amp order.
I ended up buying a 5F1 kit. I built the amp to the 5F1 layout. It sounded great as built. I didn't need to "voice it for harp". I used an old RCA 5Y3, a JJ 6V6S and a JJ 12AX7. I also used an 8" smooth cone Weber Signature Series Alnico.
I loaned the amp to a friend for a recording session and it came back sounding funny. The speaker was messed up. I ended up swapping it for a Vintage series Weber 8A125-O. Now, it sounds completely bad ass.
I ended up loaning it to David Barrett for his amp shootout a couple of years ago. It was one of the best sounding small amps in the place. Tonally, it sounded way better than the Valve Jr, Super Champ XD, Pro Jr and a couple of other small amps.
I've wanted to build a 5F2H. Every time I get ready to place the order, I keep thinking about getting a Princeton Reverb kit instead.
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Last Edited by on Jun 30, 2011 9:54 AM
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silpakorn
77 posts
Jun 30, 2011
12:22 PM
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Talking about 5F1, not that I'm gonna learn to build it anytime soon but if it's not gonna need to be voiced for harp, would this be a good idea ? - a kit with instructions from torresengineering.com
http://www.torresengineering.com/newtweed5f15.html
plus their line out kit
http://www.torresengineering.com/lineoutkit.html
Would this make it a useful little monster for a small venue ?
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5F6H
759 posts
Jun 30, 2011
2:27 PM
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The "5F1 original circuit with tone control" option sounds interesting (or even the aged 5F1 w/tone control), I would fit a tone control, or at least have a switchable hi cut cap, use the 2nd input jack for the tone pot/switch, you only need the 1Meg input anyway. The tone control can be set to drop it out of the circuit so you can go back to stock 5F1.
Line out kit - ideally you want a chassis with 2 speaker out jack holes, but it can be mounted on the amp's back panel at a push...the "line out" consists of a jack socket, 2 resistors (2.2K 1/2W & a 470ohm 1/2W) and a couple of inches of wire...Don't quite see how that runs to $15...plus delivery etc?
An amp of this type might never outlive its usefulness. Personally I might go for the mojotone kit or even the Kendrick 118 kit (this chassis is punched for a line out, it is more expensive & you need to source speaker, tubes & cab, but comes with overbuilt transformers allowing pretty well any combination of rectifier & power tubes).
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tmf714
699 posts
Jun 30, 2011
3:19 PM
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The Marsh kit is the most reasonable-Kendrick's prices are way too high-Mojotone using Orange Drops?-I guess you can get Mallories as an option,but the Marsh comes complete with cabinet, TAD filters and e-mail support,but you will need a better speaker than the stock order ceramic. Worth checking into.
Last Edited by on Jun 30, 2011 3:25 PM
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5F6H
760 posts
Jun 30, 2011
3:30 PM
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The Kendrick costs more because it uses more expensive parts...you get more possible tube options and can use the amp to test ANY octal power tube.
You pays your money & you takes your choice...
Last Edited by on Jun 30, 2011 3:44 PM
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Airstream
11 posts
Jun 30, 2011
4:55 PM
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Pick up a cheap old pa. Use an air-hose and blow out all the dead bugs and then try to find a tv repairman who is willing to help you rebuild it. I was given a broke down Chicago Webster years ago. I had no idea how I would ever get it to work. Totally frustrated by the lack of information about the amp, I decided to offer a soon to retire repairman $30 an hour to show me how to... I saw him once a weak for a couple of months. He showed me how to read a schematic, trouble shoot and stabilize the amp. I think the most important thing he taught me was to think a little bit about it first, before I move wires around.
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colynjames
20 posts
Jun 30, 2011
5:14 PM
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A good source for theory on electronics is:
http://www.electronicstheory.com/
You can easily go in to Radio Shack and order some stuff to mess around with as a supplement to learning. Just be careful when you start moving into experimenting with higher amperage stuff and live alternating current. If you respect the current, you'll be okay. Also remember that the current may not damage you, but can still damage components, so think about what you are doing before you connect wires and components and then apply power to the circuit. A lot of components are cheap...but some are not.
Educate yourself free. If you can't find free sources to train you for what you want to do, there are a lot of for hire online schools, and tons of votech schools out there with classes on the subject.
Harp amp circuits are just circuits. The build in the same basic way as any other circuit. You just need to figure out what makes a harp amp sound good and apply that knowledge to your circuit. Don't forget the importance of the speaker in the equation. I always hear guys talking about tubes and transformers, and that's part of it, but if you are searching for vintage blues tone, those speakers matter.
Happy building
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silpakorn
78 posts
Jul 01, 2011
1:02 AM
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@Joe_L, so it must be your amp then in bluesharmonica.com ? They have this amp comparison clip between Valve Jr, Kalamazoo, yours and Pro Jr I think.. and yeah, your amp sounds pretty good compare to those amps !
@tmf714, thanks for mention Marsh and Mojotone, their prices are good, have more option & come with cabinet. This might be a good start.
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Joe_L
1326 posts
Jul 01, 2011
2:26 AM
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That's the one!
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chromaticblues
901 posts
Jul 01, 2011
9:35 AM
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@airstream Man I had an old RCA from the forties and that thing sounded sweet! It looked so damn cool too. I bought for fifty $$ replaced the output transfromer and almost all of the componants and tubes. I used it twice and some guy at a gig asked if I would sell it. I told him NO! then he said would you sell it for $1000 $$. I said you bet your ASS I will. So that was the end of that. It had 4 6v6's 6j6's and 1 6SJ6. My bubby built a 4x10 cabinet that worked real well with it. I almost bought a Masco once, but noticed it looked like toast inside so well I'm sick of rebuilding everything I own. So I didn't.
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bonedog569
352 posts
Jul 01, 2011
10:39 AM
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I've learned just enough to get myself in trouble - but I did build the Lone Wolf 6l6 SE harp amp - and it is my default amp now.
books I found usefull
Dave Hunter's guitar amp handbook - some basic circuit explanations,
Jack Dar's out of print
Electric guitar amplifier handbook - keep an eye on amazon used
Elements of Radio - also out of print by Marcus and Marcus -- is a good textbook written in the late 40's
Gerald Weber books and dvds - ya gotta pick throuhg the books which are a mishmash of articles he's published - but there is some good stuff in there.
I now have this one on order
Design and Construction of Tube Guitar Amplifiers Robert C. Megantz
It got good user reviews on amazon.
the Lone Wolf amp forum is also a good resource.
Following 5F's advice
Watch some video's on how to disharge capacitors before doing anything on an amp. The stored voltages are way higher than your wall outlet.
warning - the smell of solder can become addicting - (and it's not the healthiest thing for you.)
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Last Edited by on Jul 01, 2011 10:40 AM
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silpakorn
79 posts
Jul 06, 2011
8:36 PM
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Guys, sorry to bring this up again but I think I'm all for it now, started reading some books ( Weber's & Jack Darr's ).. I know it's a long way to go before I really fully understand what you guys are talking about, about amp circuits & building but I might start building one sooner than I thought now.. just because I like tubes & getting exited about the idea of getting inside the amp & circuitry and finally build one myself. Anyway, come to my first problem right now - choosing the kit. Since the 5F1 is probably the easiest one so I think I'm gonna go with it but just the chioces of 5F1 out there can already confuse me. There are 4 companies in pretty much the same price range that I'm considering right now ; Marsh, Mojotone, Torresengineering and Tubedepot they have slight variations but when you put them together it's really difficult for me to make a decision which one would be a good start for first time builder..
This is what in my head right now :
http://store.marshamps.com/product_info.php?cPath=21&products_id=28
Good price with instruction booklet and maybe the option of 10" baffle and Weber Sig10A is a good idea ?
http://www.mojotone.com/amp-parts/amp-kits-fender-tweed-champ-style/Tweed-Champ-Style-Amp-Kit-Complete-5550001.html
Actually I'm not sure about this one.. but maybe somebody had experinced with it ?
http://tubedepot.com/kit-tweedchamp.html
The most beginner friendly I think. Over 40 pages color instruction + a youtube clip to make sure that you'll have no problem building one.. but would you consider a printed circuit board the downside ? Will I have to change the speaker to make it sound better for harp ?
http://www.torresengineering.com/newtweed5f15.html
The 8 in 1 thing is quite interesting it's just like you also purchase the options to modify it along with the original one. They also have a 10 Watts version of the champ, is it worth considering ?
http://www.torresengineering.com/hetwchki10wa.html
There you go, beginner's questions ! : ) Anyway, thanks in advance for any advice/comments.
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5F6H
764 posts
Jul 07, 2011
1:38 AM
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I would not rule out the PCB, it makes things a little trickier if you intend to be subbing components (I can make a few suggestions to be included in the initial build if you like)...but if you just want to build a working amp, with the fewest headaches, this might be the ticket.
The Torres kit is appealing due to the options & the multitap PT & the tone control (though the tone control is easily added to any of the above).
A typical Champ 125P1B power transformer has a 2A heater winding and will support a 6L6 power tube anyway, you just need to make sure that the capacitor and resistor connecting to power tube pin 8 are 100V and 10W rated respectively (there is a slight mismatch on speaker impedance but still withing the bounds of "workable" with a 6L6).
Whichever kit you go for I would strongly advise adding a screen grid resistor (1K 5W) accross power tube pins 6 & 4 and a grid stopper resistor (1.5K 1/2W) feeding pin 5 (see a Super Reverb AB763 layout for power tube wiring to see what I mean, though the SR uses 470ohm 1W instead of 1K 5W for screen grid).
If you need clarification on this you can reach me on markwjburness@btinternet.com. At the end of the day, the perceived differences between the kits makes less difference than how you execute the build & physically wire things up.
Last Edited by on Jul 07, 2011 5:40 AM
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jbone
570 posts
Jul 07, 2011
5:21 AM
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i have done very little aside from swapping a speaker and swapping pre amp and power tubes, on recommendation from other harp players. this has served to both cut feedback and also improve tone.
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