Beginner, want to build a TAD 5F1 kit

[JHow]

I think by this point we could have assembled the kit, AND copied two or three library books, and gone home to dinner.

Here is the thread I was thinking about with book recommendations:

http://music-electronics-forum.com/t18466/

[fyl]

Here's the dictionary definition

If it's a free something on the Internet it must be true.

[motzu]

If it's a free something on the Internet it must be true.

1. Rather than throwing that down from the height of your perceived position, you could have come up with a definition that contradicts the definition I found. I'm sure that pasting a definition from an Oxford dictionary you've bought would not be copyright infringement.

2. Your sarcastic comment also applies to everything you posted on this forum, so be careful not to hurt yourself in your arguments.

Why don't you just get off this thread and go report me to the House of Un-American Activities Committee already. You'll get no more replies from me.

[motzu]

I think by this point we could have assembled the kit, AND copied two or three library books, and gone home to dinner.

Here is the thread I was thinking about with book recommendations:

http://music-electronics-forum.com/t18466/

Thanks, I see Merlin Blencowe's book gets mentioned a lot, and with good reason - I've read the first chapter on his website and it's really informative. It's now in my list of future purchases.

[motzu]

OK, the kit is here, I've drilled all the relevant holes in the cabinet, chassis and eyelet board, populated the eyelet board and started soldering some components.

No problems so far understading the schematic or layout, but I do have an issue that I didn't really take into account at all, what with all the making sure I won't get electrocuted and trying to figure out how vacuum tubes work. That is, I'm baffled by how the carbon composition resistors are behaving.

To the point: I've had this bright idea of measuring all the resistors with my digital multimeter, just to make sure that if I need to troubleshoot later I'll know that it wasn't the resistors. So I look at the schematic, the resistor is 22kOhm, I measure it - it's really 23kOhm, within tolerance so OK - and I solder just one leg to the eyelet. I measure again, and now it's 45kOhm.

By now very careful, I solder only one leg of a 68k resistor on the schematic, in reality 70k. It becomes 85k after this.

Now, I will openly admit all of my shortcomings as a tube amp apprentice, but soldering is not one of them. I didn't take longer than 2 seconds in contact with the joint, and I've used the 40W Weller that's previously been approved by the nice people of the forum.

Is this something to be expected of carbon comp resistors? 10%, or within tolerance, is OK, but from 23k to 45k I do believe there's a problem with the resistors.

Your thoughts on the subject? Thanks!

[JoeM]

Did you take the resistance measurement immediately after soldering? Maybe there's a temporary increase from the soldering heat?

[motzu]

Did you take the resistance measurement immediately after soldering? Maybe there's a temporary increase from the soldering heat?

No, just took another one now (at least a couple of hours later) and it's still 45k. It seems permanent and irreversible.

I guess if they test their resistors there and find there's truth to my claim they will send out replacements, or I could just order new ones, they're not all that expensive and a Champ kit doesn't use so many of them. In your experience, is this something that's likely to happen again with new ones? Maybe I should switch to carbon film, or metal film resistors?

[JHow]

You asked for "thoughts", s here goes:

My initial thought was, does the resistance go back to spec when it cools down? Also, are these carbon composition resistors? Maybe NOS? You could try to use a clip-on heat sink if you are worried about solder heat damaging a part, but resistors are pretty robust, compared to ICs or transistors.

[JHow]

No, just took another one now (at least a couple of hours later) and it's still 45k. It seems permanent and irreversible.

Oops. Sorry, you posted while I was posting, I guess. I see they are CC. If the value has drifted that much, you probably should go with a new resistor. CF or MF will work fine.

If this is this the 1/2 watt Neg. feedback resistor we are talking about, the value isn't overly critical to function, so the amp would probably work with that part out of spec, but if this is the larger 22K in the power supply, then you will definitely want something close to spec.

[motzu]

Oops. Sorry, you posted while I was posting, I guess. I see they are CC. If the value has drifted that much, you probably should go with a new resistor. CF or MF will work fine.

If this is this the 1/2 watt Neg. feedback resistor we are talking about, the value isn't overly critical to function, so the amp would probably work with that part out of spec, but if this is the larger 22K in the power supply, then you will definitely want something close to spec.

Yes, it's an 1/2W resistor. It'll probably work like that too, but I think I'll stay safe and get new ones for all the resistors that have drifted further than 10% off spec.
Thanks!

[JoeM]

I haven't used CCs for a real long time. I'd just use CF for general purpose use.

[JHow]

In case you haven't seen it yet, I found this article interesting on the subject of carbon comp resistors and their "mojo" factor:

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

[bigsmitty]

OK, the kit is here, I've drilled all the relevant holes in the cabinet, chassis and eyelet board, populated the eyelet board and started soldering some components.

No problems so far understading the schematic or layout, but I do have an issue that I didn't really take into account at all, what with all the making sure I won't get electrocuted and trying to figure out how vacuum tubes work. That is, I'm baffled by how the carbon composition resistors are behaving.

To the point: I've had this bright idea of measuring all the resistors with my digital multimeter, just to make sure that if I need to troubleshoot later I'll know that it wasn't the resistors. So I look at the schematic, the resistor is 22kOhm, I measure it - it's really 23kOhm, within tolerance so OK - and I solder just one leg to the eyelet. I measure again, and now it's 45kOhm.

By now very careful, I solder only one leg of a 68k resistor on the schematic, in reality 70k. It becomes 85k after this.

Now, I will openly admit all of my shortcomings as a tube amp apprentice, but soldering is not one of them. I didn't take longer than 2 seconds in contact with the joint, and I've used the 40W Weller that's previously been approved by the nice people of the forum.

Is this something to be expected of carbon comp resistors? 10%, or within tolerance, is OK, but from 23k to 45k I do believe there's a problem with the resistors.

Your thoughts on the subject? Thanks!

You have to measure resistor out of circuit for a true reading.

[motzu]

You have to measure resistor out of circuit for a true reading.

You're right, and I did. The first thing I did was to pull out the resistor and measure it by itself. It's 45k.

[bigsmitty]

You're right, and I did. The first thing I did was to pull out the resistor and measure it by itself. It's 45k.

Cool! just making sure, wasn't clear from your post. I guess you need a new resistor then. unless its the NFB you might like it that way.