Tube Amp Archive

I was thinking such as; 2.7K/.68uf for example. How would that sound in a tweed champ? Less fat, less gain and an enhanced bright effect. Are you saying less gain because of the 2.7K? Would a .68uf cap well with the 1.5K? Just wondering about the "knee" or cutoff of the combination. I don't want to...

I initially had no cap on my tweed champ I just built. It needed one. So I installled a 4.7uf. It has great gain but a little muddy. I'm using the 1.5K resistor. For less mud at top volume, if I went down to 1uf or less, would the resistor have to be increased? I know there is a relationship there a...

Yes, the switch is connected and the tubes appear to be glowing normally. I will check the voltages of each tube.

I'm thinking it does have a center tap. It has the red/yellow wire which is attached to ground. It also has the 2- 100 ohm resistors, which are attached to ground. Measuring across the wires, instead of to ground, I got the full 6.3V and 5.4V. So the problem must be the builder! Not sure what I did ...

[img[IMG:1024:764]http://i1243.photobucket.com/albums/gg557/jdw33/Champ%20New%20PT/IMG_0613.jpg[/img] [IMG:1024:764]http://i1243.photobucket.com/albums/gg557/jdw33/Champ%20New%20PT/IMG_0612.jpg[/img] [IMG:1024:764]http://i1243.photobucket.com/albums/gg557/jdw33/Champ%20New%20PT/IMG_0611.jpg[/img] [I...

I built a Mojotone tweed champ and for whatever reason, the first PT didn't work. So they sent me a new one. They were nice about it. I installed the new one and I have proper voltage on the red wires to rectifier, 330V. Green heater wires are about half what they should be; I have 3.3V per wire. Sp...

I'm sure I mentioned this in another thread, but I should add this here. I added 2.2K/2W screen resistors to the BassMate. It fired up and so far no problems. Lost a bit of volume, which is fine, and possibly a bit of gain. It sounds great though. Tubes are not pulsing with chords or anything. Thank...

I'm sure I mentioned this in another thread, but I should add this here. I added 2.2K/2W screen resistors to the BassMate. It fired up and so far no problems. Lost a bit of volume, which is fine, and possibly a bit of gain. It sounds great though. Tubes are not pulsing with chords or anything. Thank...

My approach would be to increase the 470 ohm Screen B+ node supply resistor to 1k or 1k5, and use smallish individual screen grid stoppers, mounted on the tube bases, eg 220 or 470 ohms. That minimises the local negative feedback, gain / power compression. What difference does the amp "see", compar...

How do you measure plate voltage/screen voltage? If I get the readings at idle, how do you know where they are under load? A signal generator?

hired hand wrote:FWIW.....
On an AC15 type amp I just built, I used (out of necessity) 2k7 1 Watt screens with JJ 84's.
best

How did you come to 2.7K? Just trying wrap my brain around the math.

So, I installed the cap and screen resistors. Amp sounds great.

Just wondering what the cap or lack of it would do to the amp.

Ok, I installed screen resistors in my '70 Traynor BassMate, which burned up tubes and popped fuses. I used 2.2K@2w. These are after the stock 470ohm resistor on the board. The amp sounds great! A little quieter but not really any tonal change. I cranked it for a minute and the tubes didn't even qui...

Would the same apply for el84 types? I'm trying to decide what size screen resistors to use; it has a single 470ohm feeding both tubes.

Is the 470, combined with 2.2k at each tube, too much resistance?

xtian wrote:Check my thread on my recent YBA-2 build:

https://tubeamparchive.com/viewtopic.php?t=20310

Mine is stable.

I did see that. Very nice work. I have that amp as well, slightly modded for guitar. Everyone loves that sound! Mine is the 1x15 combo.