Amp Complete, Little help please!

[danielarimcaulay]

Hi,

Finally finished my 5E3 last night. spent a few h ours troubleshooting untill I found my guitar lead was faulty!!(Newbie error)

The Amp is working, only a small amount of hum.
BUT, Both of the normal inputs seem to be unaffected by either volume pot. I have checked all the pots and they all seem to still be functioning linearly to 1 Meg.
Bright Inputs for both channels working fine, I find a lose of tone if the "other" volume pot is turned past 3 O clock.

The amp is also VERY clean. Still rather loud but not dirt at all.

The amp circuit is stock standard, With the exception of the Gz34 rectifier and the pre-amp is 2x JJ Ecc83s, Power tubes are JJ6V6s. B+ 400V

Any suggestions would be greatly appreciated.

Also a silly question. Are the two volumes for inputs 1 and 2, or for Bright and Normal?

Im also trying to check my power. I came up with 19watts so guessing i'm wrong or going to cook something.
I have 24.0 volts dropped across my 250.0 Ohm, Which gave me 96mA. So do i half that current as there is two tubes? so 48mA then multiply that to my B+ to get power?? Sorry for all the question. This is all rather new to me!

I have attached some pictures.

Dan

[tubeswell]

May I suggest that you either increase your cathode resistor until the combined current is around 72-76mA (yes you halve if for the current-per-tube), or put a 5Y3GT or a 5V4 rectifier in. The output tubes are cooking themselves the way you have it set up at the moment

[danielarimcaulay]

Thanks for the reply,

I did some research, and turns out I'm making 15.8 watts. Am i right that JJ6v6 can handle 16W? All would increasing to a 330ohm me wise?

I found I had a dry solder joint on one of my volume pots. Fixed that and both input volumes working. The volume seems to be silent then very loud. Its almost impossible to run the amp at a bedroom level. Is this normal? or is there a way to have more control of the volume at lower levels?

Thanks in advance

Dan

[Tom Phillips]

...The volume seems to be silent then very loud. Its almost impossible to run the amp at a bedroom level. Is this normal? or is there a way to have more control of the volume at lower levels?...

No. That's not normal. My first guess is that you have used linear taper pots for the volume controls instead of audio taper. Are you familiar with the difference?

Tom

[danielarimcaulay]

Familiar with the difference, The pots are linear. This amp was built from scratch. I was under the impression all 5E3 amps had linear pots?

[Tom Phillips]

The old 5E3 schematics don't indicate the taper at all.
I would have assumed audio taper.
Let's see if anyone else chimes in.

[danielarimcaulay]

I had a play today with some new parts.
I replaced the Pots to to 1M log and didn't make any noticeable difference to the sensitivity of the volumes.
Replaced the cathode resistor with a 330 and it bought the power down to 14.0 Watts.

I also find playing through the Normal inputs, I must have the 2nd volume turned up to around "2" before the 1st volume knob starts having an effect. One volume is very sensitive and the other volume is almost like a fine volume control!
Any ideas would be great.

Dan

[Philr228]

Well done on completing your build, I too have just completed my scratch build too, with it all working beautifully, very clean, cleaner than expected but I like and want that, but I'm running my output tubes a little hot too.

Check out my thread to view all the calculations regarding power dissipation from a very knowledgable source 'Loudthud'!

http://music-electronics-forum.com/t15558/

Just a note how are you grounding the three pots left terminal (viewed from the back, tone thru cap) . They seem to daisey chain back through each other and not sure where they ground. You could ground each to the back of each pot. assuming they are grounded to the chassis or brass plate!

Phil

[guitician]

Are the un-grounded sides of the volume controls common with the tone controls center connection and the grid of the 12ax7?

[loudthud]

OMG !!!

Is that a Printed Circuit Board ???

[danielarimcaulay]

Is that a Printed Circuit Board ???

Yea
I know its not the normal for a tweed. But my idea was to "base" my amp around the 5e3, Not build a clone!
It seems to work very well. The layout is almost identical with a few changes to the where some resistors lay. The only problem I have found so far is that to change the value of a resistor you need to "through hole solder" as I'm to lazy to remove the whole board!

Opinions?

I found the problem with the volumes. I wired up to lead revered when swapping the pots for the Logarithmic ones. Nearly no interaction between volumes now. But they are still VERY sensitive.

Some more photos of the Amp.

[danielarimcaulay]

...and I have to add. Who ever spread the word on the artificial centre tap in regards to the heater wires with the 100ohm resistors is a legend. I disconnected them while fault finding for a few minutes. Those resistors get rid of ALOT of hum. Many thanks to everyone's help on this forum.

[tweed]

Hi there, the cabinet looks very cool. Can you explain how you calculate the amp power?

Thanks

[danielarimcaulay]

Hi there, the cabinet looks very cool. Can you explain how you calculate the amp power?

Thanks

Thanks, I was thinking about covering it in tweed. I think I'll leave it wood at this stage though!
I calculated power by measuring the current through the cathode resistor. Halving that figure and then multiplying to the plate to plate voltage.
Im not 100% if that's the correct way. But gives me a 13.9 watts.

I have yet to find any overdrive in my amp. Its so loud witht the volume set at "2" I haven't had the balls to crank it up above "3"!

[tweed]

You should start to get some break up around 4 with your guitar's volume all way up. Although this amp is pretty loud. See this post, gibson lp studio pluged straight: http://music-electronics-forum.com/t15463/#post125984

At this moment when I want more clipping at very low volumes, I use an Overdrive pedal to clip the signal and I control the volume in the pedal. It's not comparable with power tubes distortion but it still has the 5e3 circuit and alnico speaker in the mix... I can get really nice tones.

The correct way to do it is placind an attenuator placed between amp and speaker. You can set your amp to give the tone you're looking for and reduce the overall volume. I just got one on ebay, I am looking forward to try it.