The Amp Garage

I know it is not a tube amp but I could not see another area for this question so I hope the mods understand. I have checking to see if anyone has one of these amps and if so, could I get a Flashrom/Serprog to read the data on that amps serial mem chip? I need that information to try and revive a de...

Phil, Below is how in their document they come up with a calculated ma. So here are my values and I italicized the section from the document for measurements that I used. 17.5/426.5 = .0410 = 41.0 3) Let's say that you want to bias the amp for 70% of the maximum plate dissipation of the power tube(K...

Well since you folks showed me what was wrong when I was trying to use the “shunt” method and I am very aware of the what lyies inside the box I tried it out using all safety precautions. So using the Marstan shunt bias method below is what I came up with. And of coarse DO NOT TRY THIS METHOD IF YOU...

Swapped and now down to about a 4ma difference.

Will do.

I know I have swapped them before but I took them out while working on so I cannot remember who was where. Stinks getting old!

So I just hooked up my meters (Fluke 115 and a cheap one) to check the bias and I am coming up with a 6ma difference between this set of matching Mullard XF2 tubes. V5 is giving me the higher reading and it does not matter what meter is on which tube, same reading. I am just not sure if this points ...

Lynxtrap, My I ask why it worries you? I'm not so worried anymore :) At that point I knew nothing about your experience with electronics and working around potentially lethal voltages. Those other methods of measuring bias can be dangerous, and it appeared that you lacked some understanding of how ...

It can be difficult to get an accurate reading on a 1Ω resistor. If they are spec'd at 1%, which is about as good as it's going to get, then they are probably just that. If you cross your meter leads, what does the meter read? I believe this tells you about the low end reading it can manage with ac...

Well the 1 ohm 1% resistors are back in place. One of them read 1.1 ohm and one read 1.2 ohm. I will start some measurements either tomorrow or Friday since I have a med appointment tomorrow. I greatly appreciate all of your concerns. This may be my first amp build but not my first run around with c...

Lynxtrap, My I ask why it worries you? This is my first amp build and I tried to read everything I could on this subject but felt it necessary to ask for help. And if you say that with the best intentions, that is how I will take. I have no issues what so ever in dropping thos resistors back in. Abo...

And why not leave the resistors in place so you have the option? As I said above, they won’t affect the results you’ll get using the OT primary resistance method. Nowhere in any document I read or got from anyone else, that it is OK to drop the resistor just place a piece of wire in it’s place. I’l...

sluckey wrote: ↑Wed Mar 06, 2019 3:58 am I'm very curious... Why don't you want to bias that amp using the very good and simple instructions on page 28 of the instruction pdf?

Doing some reading of bias methods, I had read there were two more accurate ways to accomplish it, so I wanted to give them a try.

Thank you guys SOOOOO much.

Yes, that is what I what missing. Nowhere in any document I read or got from anyone else, that it is OK to drop the resistor just place a piece of wire in it’s place.

Thanks again since I thought I was loosing my mind!

Now I will give it a go tomorrow or the next day.

Martin, Thank you for the reply and information. That is my problem, when I have the amp powered on, I get absolutely no voltage reading from the OT centertab/B+ turret to pin three of either power tube, while look8ng for a voltage drop. I can set my fluke to auto, manual, whatever and nothing for a...

Phil,

Thank you very much for the reply and I apologize I did not document that I removed those one ohm resistors, since those in the system I cannot do the biasing in the way I outlined above.

My apologies again, James