Tweed Champ (5F1) in Europe?

[red]

I've started wiring the input transformer to the rectifier tube. Here's a TAD picture of the rectifier tube wiring:



What I'm not clear on is this: the layout says I should wire the two yellow wires to pins 2 and 8, and the two red wires to pins 4 and 6. But they don't say which of the pair goes where. I'm assuming that it doesn't matter? Any of the yellow wires can go to either pin 2 or 8, and any of the red wires to 4 or 6?

[tunghaichuan***]

I've started wiring the input transformer to the rectifier tube. Here's a TAD picture of the rectifier tube wiring:



What I'm not clear on is this: the layout says I should wire the two yellow wires to pins 2 and 8, and the two red wires to pins 4 and 6. But they don't say which of the pair goes where. I'm assuming that it doesn't matter? Any of the yellow wires can go to either pin 2 or 8, and any of the red wires to 4 or 6?

The yellow and red wires are not polarized, it doesn't matter which yellow wire goes to pin 2 or pin 8 and it doesn't matter which of the red wires goes to either pin 4 or 6.

Also make sure you twist the yellow leads together and twist the red leads together as shown, this helps in noise reduction as both the yellow and red leads are AC.

[tunghaichuan***]

Do you mean after the first 3 caps, reading the layout left to right, and in parallel with the 4th cap? The kit comes with a green 5W 470 5% resistor there.

To clarifiy:looking at the first photo on this page:

http://www.tubeampdoctor.com/newsdes...newsdesk_id=40

To put in a screen grid resistor, go to the eyelet for the second cap from the left, the one where the green and brown resistors are. You would solder in the end of a 470 ohm 2-5W resistor there (in addition to the two already there) and solder the other end to pin 4 on the 6V6 tube socket.

[red]

Also make sure you twist the yellow leads together and twist the red leads together as shown, this helps in noise reduction as both the yellow and red leads are AC.

Of course, AC isn't polarized, and it's the input transformer . Now I can apply for a special bus pass.

Twisted and connected. Thanks!

[red]

To put in a screen grid resistor, go to the eyelet for the second cap from the left, the one where the green and brown resistors are. You would solder in the end of a 470 ohm 2-5W resistor there (in addition to the two already there) and solder the other end to pin 4 on the 6V6 tube socket.

OK, I did get that - I just thought that by "decoupling resistor" you meant the second green resistor from their picture. BTW, my kit came with one green resistor (the 5W one connected in parallel with the 4th cap). The one connecting the legs of the 1st and 2nd cap is a carbon comp 1W/10k. Hopefully it won't change its resistivity rating when soldering, as I don't have a replacement for it.

I thought about using a clip-on heat sink of some sort (most likely a plain alligator clip) when soldering the next resistors, but I keep wondering if that will solve anything since once I power up the amp the resistors will get current flowing through them with likely similar effects.

[red]

And now they got me a bit confused again. In this picture:



The blue wire coming from the output transformer connects to the power tube socket, and the red to the eyelet board. But in the layout they printed out and sent with the kit, it says that the red goes to the tube socket and the blue to the eyelet board. This is probably a mistake, since A. the pictures are somewhat proof of a working amp, and B. I've looked up several other layouts on the Internet for a 5F1 and they all said that the blue wire goes to the tube socket and the red to the board. I've sent an email to TAD trying to make sure before I melt solder there - they'll likely reply on Monday.

The other wires from the output transformer I've connected thus (as per their layout): black to ground, green to tip (black to ground seems to be a common theme with the speaker wires too).

[tunghaichuan***]

And now they got me a bit confused again. In this picture:



The blue wire coming from the output transformer connects to the power tube socket, and the red to the eyelet board. But in the layout they printed out and sent with the kit, it says that the red goes to the tube socket and the blue to the eyelet board. This is probably a mistake, since A. the pictures are somewhat proof of a working amp, and B. I've looked up several other layouts on the Internet for a 5F1 and they all said that the blue wire goes to the tube socket and the red to the board. I've sent an email to TAD trying to make sure before I melt solder there - they'll likely reply on Monday.

The other wires from the output transformer I've connected thus (as per their layout): black to ground, green to tip (black to ground seems to be a common theme with the speaker wires too).

The blue and red wires are the 6v6 plate/anode and B+ connection.

Since you have negative feedback in this amp, it matters which color wire goes where. Technically speaking hooking up the wires one way will put the primary of the output transformer in phase with the secondary. If you hook up the red and blue wires out of phase, you will have *positive* feedback injected into the amp and it will squeal as it is turned up.

So you have two choices if you wire it incorrectly: 1. switch the primary wires (blue & red) or switch the secondary wires (don't know what color you have but the US standard is black and green.) It might be easier to switch the output (secondary wires) since they are on the jack.

This was one of the first things I learned when I built my first 5F1 about 15 years ago. The output transformer was wound so that the blue was B+ and red was the plate connection. I hooked them up in reverse order, normally the standard: red as B+ and blue as plate/anode. Squeal city. At the time it was easier for me to switch the secondary/output wires, so that green was grounded and the black wire when to the hot/tip of the output jack.

If you want to be sure, email TAD and ask them what the correct color coding is.

[red]

So you have two choices if you wire it incorrectly: 1. switch the primary wires (blue & red) or switch the secondary wires (don't know what color you have but the US standard is black and green.) It might be easier to switch the output (secondary wires) since they are on the jack.

Yes, the secondary wires are green and black. I've mentioned them in my previous post (wired: green to speaker jack tip, black to ground), but I've obviously got a lot more to learn (about tube amp terminology and technology) and English is not my first language, so I guess sometimes I'm not as clear as I could be - sorry.

If you want to be sure, email TAD and ask them what the correct color coding is.

I did already email TAD, but they won't answer until Monday probably. But you've made the correspondence between the primary and secondary wires pretty clear, so if I had to get it done quickly it wouldn't be much of a gamble. As it stands, I have to wait anyway for a new batch of resistors I've ordered to replace the ones in the kit that changed resistivity more than what the tolerance band spec'd - so hurying to solder the output transformer wires won't make much of a difference with regard to the power-on day. I'm just trying to ask questions and learn as much as possible.

Thank you, I really appreciate your help! If you ever write a book about tube amps, autograph the first copy for me and let me know where to send the money.

[red]

This was one of the first things I learned when I built my first 5F1 about 15 years ago. The output transformer was wound so that the blue was B+ and red was the plate connection. I hooked them up in reverse order, normally the standard: red as B+ and blue as plate/anode. Squeal city.

Looks like that would have been my fate as well, had I decided not to email TAD and be too smart for my own good about it. They've answered my email, and apparently the pictures on their website have been taken a long time ago when they were shipping the kits with a different output transformer. So just in case anyone else trying to build a TAD 5F1 Champ stumbles across this thread: take the layout's word over the pictures on the website. In my case, red goes to the power tube plate and blue to B+.

Went out hunting for a metal oxide 470 Ohm resistor today, the local shops did not carry any 2W ones, but I've managed to find a 3W 470 Ohm metal oxide resistor. I guess that should do fine.

[red]

Another thing, the TAD schematic specifies voltage at various points in the circuit, measured with DVM read to ground. At one point it even goes up to 390V. Now, if I do that measurement I will do my best to stay safe (clip one DVM to the chassis and tape the other lead to the end of a wooden chopstick) - but my digital multimeter is a cheap one, and the probes look like this:



My DMM is a Velleman DVM850BL (click for specs). Supposedly it can handle up to 600VDC, but looking around on the Internet I came across the concept of a "high voltage probe". Do I need a pair of those? Should I go out and buy them or just skip the measurement step altogether if the amp powers up and works?

[red]

I've decided to stick to carbon comp resistors just because Victoria uses them and I love the way the 518 sounds. They're probably overkill to use all over the place, but it makes my life simpler, and if the noise they add won't be more than what the 518 puts out, I'll be happy.

I've sourced some new carbon comps (still waiting for a couple of 100k ones that turned out to be harder to get) and started wiring the board and soldering them in place. This time no surprises with the resistivity rating after soldering.

But - the two 68k grid resistors came at 71-72k and turned 73-74k after soldering. And the 220k power tube grid load resistor came at 250k and went to about 254k after soldering.

I don't think that either drift is spectacular or particularly important for the well-being of the finished amp, but as CCs will do, they will most likely continue to slowly drift upwards. The two "68k"s won't make a noticeable difference, but I'm worried about the "220k" - what if it goes to 300k? I'm assuming it won't affect the tone but will affect the power tube "loudness", and the power tube itself.

Hmm, maybe that's actually a good place for a metal or carbon film. If I understand it's purpose correctly, no signal actually goes through that resistor, except maybe to "go away" to ground.

[tunghaichuan***]

Don't worry about the slight increases in resistance. Those old carbon comp resistors are typically +/- 20% so they can be 20% under or over the value and not cause any problems.

I checked the data sheet for the 6V6 and the maximum resistance for the grid load resistor (the 220K) is 500K, so at +/- 20% you're well below the max.

The main problem with carbon comps is that they drift in value over time compared to metal film, metal oxide, or carbon film resistors. Sometimes when they drift just right the amp sounds very good. Other times, it doesn't doesn't work out so well. That's partially why some vintage amps sound great and others don't.

They can be noisy in certain positions, such as the plate load (100K). But some think that there is some magic/mojo if you put carbon comp resistors in those positions. I have not tried it myself, but I think it would be hard to tell the difference in a double blind test.

I've decided to stick to carbon comp resistors just because Victoria uses them and I love the way the 518 sounds. They're probably overkill to use all over the place, but it makes my life simpler, and if the noise they add won't be more than what the 518 puts out, I'll be happy.

I've sourced some new carbon comps (still waiting for a couple of 100k ones that turned out to be harder to get) and started wiring the board and soldering them in place. This time no surprises with the resistivity rating after soldering.

But - the two 68k grid resistors came at 71-72k and turned 73-74k after soldering. And the 220k power tube grid load resistor came at 250k and went to about 254k after soldering.

I don't think that either drift is spectacular or particularly important for the well-being of the finished amp, but as CCs will do, they will most likely continue to slowly drift upwards. The two "68k"s won't make a noticeable difference, but I'm worried about the "220k" - what if it goes to 300k? I'm assuming it won't affect the tone but will affect the power tube "loudness", and the power tube itself.

Hmm, maybe that's actually a good place for a metal or carbon film. If I understand it's purpose correctly, no signal actually goes through that resistor, except maybe to "go away" to ground.

[red]

Don't worry about the slight increases in resistance. Those old carbon comp resistors are typically +/- 20% so they can be 20% under or over the value and not cause any problems.

I checked the data sheet for the 6V6 and the maximum resistance for the grid load resistor (the 220K) is 500K, so at +/- 20% you're well below the max.

The main problem with carbon comps is that they drift in value over time compared to metal film, metal oxide, or carbon film resistors. Sometimes when they drift just right the amp sounds very good. Other times, it doesn't doesn't work out so well. That's partially why some vintage amps sound great and others don't.

They can be noisy in certain positions, such as the plate load (100K). But some think that there is some magic/mojo if you put carbon comp resistors in those positions. I have not tried it myself, but I think it would be hard to tell the difference in a double blind test.

Once again, a quick and very clear answer! If you're ever in Romania, let me know because I owe you some glasses of your favourite beverage

I'm sorry for my novice questions, I'm learning as fast as I can and it's quite a lot to absorb. I've looked everywhere BUT at the 6V6 data sheet. Sometimes I get a bit tired with the research and the everyday stuff, that I tend to overlook obvious things...

I've read R.G. Keen's article about carbon comp resistors and he seems to make a case for the mojo factor. If that's one of the main differences between how the Swart Space Tone 6V6LE (which I've only heard online) and a Victoria 518 (which I've played) sound, there's definitely a warmer vibe to the Victoria. Not that there's anything wrong with either approach, just a matter of taste.

Any opinion on whether I should try to check the voltages inside with my cheapo multimeter/probes?

If anyone else stumbles upon this thread and needs more info about the 5F1, here's a very nice explanation of the preamp stage in a 5F1: http://www.classictubeamps.com/preamp.html

Thanks again, tunghaichuan!

[tunghaichuan***]

Once again, a quick and very clear answer! If you're ever in Romania, let me know because I owe you some glasses of your favourite beverage

I'm sorry for my novice questions, I'm learning as fast as I can and it's quite a lot to absorb. I've looked everywhere BUT at the 6V6 data sheet. Sometimes I get a bit tired with the research and the everyday stuff, that I tend to overlook obvious things...

No problem, glad to help out. Definitely Google the 6V6GT data sheets. FWIW, the 6V6GTA is the same tube but is rated as a 14W tube for maximum dissipation. The 6V6GT is only rated at 12W. The "A" designator means slow warmup for use in tube equipment that runs the filaments of the tubes in series. (Filaments are wired in parallel in the 5F1.) The 'GT is identical to the 'GTA except for the "A." The 14W vs. 12W discrepancy is due to the way the tube industry rated the tube. You'll need this number if you want to check the bias of your 6V6 tube. Be aware that the JJ/Slovak 6V6S is not really a 6V6 tube, it can dissipate up to about 18 watts or so so it is more like a metal 6L6 or 6L6G in terms of power dissipation.

The bottom line is that some 6V6 tubes can be biased up to 14W with no problems, while other will over dissipate ("red plate") and will have to be biased down to 12W.

I've read R.G. Keen's article about carbon comp resistors and he seems to make a case for the mojo factor. If that's one of the main differences between how the Swart Space Tone 6V6LE (which I've only heard online) and a Victoria 518 (which I've played) sound, there's definitely a warmer vibe to the Victoria. Not that there's anything wrong with either approach, just a matter of taste.

RG Keen has forgotten more about electronics and tube circuits than I'll ever know, so I will defer to his judgment on this

Any opinion on whether I should try to check the voltages inside with my cheapo multimeter/probes?

That meter should be fine. When measuring the B+ or any other high voltage DC use the 600V setting set for DC. If you want to measure the raw AC coming out of the PT, use the 600V setting set to AC and measure from one end of the high voltage lead to the center tap. Don't measure across the entire HV winding or you might burn out the meter.

To measure cathode voltages, set the scale to the nearest appropriate voltage level on the DC setting. There is about 1v on the 12AX7 cathodes and about 20V or so on the 6V6's cathode.

You might want to get a set of retractable hooks for the meter. One for the black and one for the red lead. You can hook up the black lead to ground and then measure the voltages with one hand. Put the other hand in your pocket or behind your back as a safety precaution.

If anyone else stumbles upon this thread and needs more info about the 5F1, here's a very nice explanation of the preamp stage in a 5F1: http://www.classictubeamps.com/preamp.html

Thanks again, tunghaichuan!

Thanks for the link, I had not seen that site before.

[red]

RG Keen has forgotten more about electronics and tube circuits than I'll ever know, so I will defer to his judgment on this

Oh I'm sorry, I thought the link to the article had already been posted somewhere in this thread. Here it is:

http://www.geofex.com/article_folder...carboncomp.htm

You might want to get a set of retractable hooks for the meter. One for the black and one for the red lead. You can hook up the black lead to ground and then measure the voltages with one hand. Put the other hand in your pocket or behind your back as a safety precaution.

Yep, that's the plan. Thanks!

[red]

Another noteworthy piece of information I've come across is that Victoria and the Weber 5F1 kit use a 25uF capacitor in parallel with the 1K5 resistor coming from pin 3 of the 12AX7.

Here's the Weber 5F1 layout:

http://taweber.powweb.com/store/5f1_layout.jpg

And a short film from Victoria humorously illustrating a 5F1 build:

http://www.youtube.com/watch?v=1xj6d9MLCpo

Supposedly this is a bypass cap, added in order not to screw up the 12AX7 bias as far as DC goes, but boosts the mid and low frequencies (or rather cuts some of the high ones?) in the AC current.

In any case, I don't have a quality electrolytic capacitor to add there, and I'm fed up as it is with waiting for parts so I'll just try the 5F1 I have as soon as I can, and if there'll be any problem with the tone I'll make that adjustment then.

[tunghaichuan***]

Putting a cathode bypass cap across that 1.5k resistor is a common mod. I believe that some 5F1 Champs came out of the factory with it, stock, although it was not on the schematic.

You can use values from .68uF to 22uF. The practical range is from 2uF-4uF for humbucking pickup guitars and 4uF-10uF for single coil equipped guitars.

Another noteworthy piece of information I've come across is that Victoria and the Weber 5F1 kit use a 25uF capacitor in parallel with the 1K5 resistor coming from pin 3 of the 12AX7.

Here's the Weber 5F1 layout:

http://taweber.powweb.com/store/5f1_layout.jpg

And a short film from Victoria humorously illustrating a 5F1 build:

http://www.youtube.com/watch?v=1xj6d9MLCpo

Supposedly this is a bypass cap, added in order not to screw up the 12AX7 bias as far as DC goes, but boosts the mid and low frequencies (or rather cuts some of the high ones?) in the AC current.

In any case, I don't have a quality electrolytic capacitor to add there, and I'm fed up as it is with waiting for parts so I'll just try the 5F1 I have as soon as I can, and if there'll be any problem with the tone I'll make that adjustment then.

[red]

It works! It sounds good "out of the box" , but it's getting better fast - the filter caps are probably settling in, maybe some undecided carbon comp resistors still figuring out what value they want to be, and definitely the speaker getting more and more in a vibrating mood.

Thanks for all the help, tunghaichuan!

[tunghaichuan***]

Glad to hear everything worked out for you. It may take a while for the speaker to break in, but it will only get better sounding. Great job, I like the looks of that little amp.

It works! It sounds good "out of the box" , but it's getting better fast - the filter caps are probably settling in, maybe some undecided carbon comp resistors still figuring out what value they want to be, and definitely the speaker getting more and more in a vibrating mood.

Thanks for all the help, tunghaichuan!