Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mr. P ~ on January 16, 2015, 12:17:59 pm
-
I just finished building my first chassis which is a Fender Champ. After playing it a while it seems to have too much Bass. I am playing it through a closed back 2X12 cabinet. I found someone playing their champ through a 4X12 cabinet and it seemed to have plenty of treble but mine through 2 12s only sounds good on the bridge pick up. MY Question: Should the tweed champ seem to have too much bass if played through multiple 12s or is it voiced for an 8" speaker? :w2:
-
Which champ? If it's the 5E1 you can replace the 25µF cap on the cathode of the first preamp tube with something smaller, maybe 1µF to 5µF. Or just remove it completely, like the 5F1.
PS, red fonts on a gray background is hard on some old eyes.
-
Thanks for the response. Actually I built the 5F1 circuit so the 25mfd is not there. Maybe the ones I listened to were 5E1 circuits.
Odd about the color, I have had someone mention the red font issue before. I don't understand what the problem is or what causes it and it doesn't affect my 62 year old eyes. This should work better.
-
my 58yr 'ol eyes sees almost a 3d or embossed effect. I built a 5e1ish and it wasn't bass enough so I played with the 2 tone caps till I was happy, think I used .05 and 500pf
-
I had glare problems and various double vision issues till I got my cataracts fixed. Most of that sort of thing is no longer a problem.
-
What is the bias set at? Post up the voltages on every used pin on the 6V6 and tell the value of the cathode resistor. Are you using a double humbucker guitar, and plugging into the right hand input jack? Double humbucker guitars like the Les Paul are notoriously dark sounding through low gain amplifiers and need to be plugged into the low impedance jack. A lot more info is needed to understand and help determine why you have more bass response (perceived or otherwise) than normal. The tweed amps generally produce more midrange frequencies. If you are using the stock 470 ohm value on the cathode (bias) resistor of the 6V6 you may be running way too much current through the tube and it can cause abnormal sound. Have you installed a grid stopper resistor and a screen resistor? These are not shown on the schematic but most guys run them these days.
-
I have the standard 470 ohm bias resistor and yes I am using twin humbuckers (Guild Bluesbird). I wondered if there was a guitar related issue like the humbuckers. The Grid stopper and screen resistor were on my list to try but I expect it is the pickups....it sounds like I was using bass guitar speakers. Thanks. I will get the voltages tomorrow.
-
What tubes are you using? What is the rectifier specifically? Is it a Sovtek 5Y3?
The grid stopper is there to reduce or eliminate parasitic oscillations as well as other effects. The Screen grid resistor is for safety and proper power tube operation.
Discussion here technical discussion (http://www.valvewizard.co.uk/gridstopper.html)
-
Thank you sir. Looks like it's just what I needed.
-
Hi, just want you to be aware that is you are using a Sovtek or a GT 5Y3 rectifier that they are not a real 5Y3 and have way less voltage drop and produce much higher voltage. Paired with the fact that mains voltage is now higher in most places in the US the high voltage on the PS rail can approach and exceed 400v easily. If you have very high plate volts your 6V6 could be running quite high current with the stock 470 ohm cathode resistor. I have been using real 5Y3 rectifiers and adding an additional Pi filter setup to get the rectified voltage and current down. Also my typical bias resistor is between 620 and 1K. I suppose if you are using a vintage 6V6 or a JJ 6V6 then the danger is lessened somewhat.
This is why I asked about the voltages on your 6V6.