5E3 help/advice needed

[stephenhartley]

Hi

I've just finished my second 5E3 build. I've put in the 6G3 tone circuit so that there's a separate tone and volume for each channel. Apart from that it's a stock circuit.

When I switch on there's a fairly loud buzz which is modified by the tone and volume controls.

I've disconnected the tone circuits and channel two leaving just the vol from channel 1 feeding pin 2 of V2.

The buzz remains, but disappears when the volume is around 8/10 - it returns when I turn it up full or below 8.

I've carefully checked all the wiring against the schematic and now I'm stuck - I don't know what to do next.

Could it be an earth problem?

Any advice would be greatly appreciated

[loudthud]

Gonna need to see a layout showing how you wired up ground or some clear well lit pictures.

[soundguruman]

Hi

I've just finished my second 5E3 build. I've put in the 6G3 tone circuit so that there's a separate tone and volume for each channel. Apart from that it's a stock circuit.

When I switch on there's a fairly loud buzz which is modified by the tone and volume controls.

I've disconnected the tone circuits and channel two leaving just the vol from channel 1 feeding pin 2 of V2.

The buzz remains, but disappears when the volume is around 8/10 - it returns when I turn it up full or below 8.

I've carefully checked all the wiring against the schematic and now I'm stuck - I don't know what to do next.

Could it be an earth problem?

Any advice would be greatly appreciated

I mean, you could not tell without seeing it.
But there may be a crack in the volume pot, or a broken ground connection somehow.

[stephenhartley]

Thanks for your replies.

I've used the standard schematic and layout from Weber's book, and just pencilled in the 6G3 tone circuit.

I haven't followed any particular pattern with the earths - I've just done the same as I did with my first build and routed them mainly to the transformer bolts.

I have read bits on here about different positioning of earths, but have never understood it - is the chassis not just one common earth.

I'll put up some pics later

[stephenhartley]

I've now been through all the earths and redone them as per the Ceriotone circuit as advised on here.

I've replaced all the wires from the input sockets to the 68K resistors with screened wire, earthing the screens to the pot earth lug and joining the screens at the other end.

The wire from the 2 220k bridging resistors to pin 2 on V2 is screened. The screen is earthed to the pot and free at the other end.

Still no difference - the loud buzz persists and is modified by the tone and volume controls - the amp itself (through a celestion alnico blue) sounds awesome.

Any advice greatfully received - I don't know what to try next.

I've tried to upload 8 pics but can't - keep getting the message 'you do not have sufficient permission to perform this action - please refresh page and log in again - have done this, but still can't upload pics. Any suggestions?

[stephenhartley]

Managed to upload pics - needed to enable cookie

[Steve Conner]

Where is the centre tap of the HT winding connected? If it's just routed to a transformer bolt, try connecting it directly to the negative terminal of the first filter cap. That is, the same filter cap whose positive terminal has the cathodes of the rectifier diodes.

[stephenhartley]

Thanks - I'll give that a try. The HT centre tap is currently grounded to a transformer bolt along with the mains earth and the OT output zero. It's actually a 5Y3 tube rectifier.

The other earths are all grounded to a separate chassis bolt (as per the Ceriotone 5E3 circuit)

[stephenhartley]

Tried it - unfortunately no difference

[stephenhartley]

The buzzing is affected by the tone and volume controls and almost disappears when then bright channel tone control is about 8. ?

[Bruce / Mission Amps]

To eliminate a bad or improperly wired input jack or bad volume pot in these...
Take two clip leads and ground the end of each.
Now clip the other lead to lug 2 of the first preamp tube and do your test... no difference?
Leave it and clip the left over clip lead to lug 7 of the first preamp tube... no difference...?

Remove one from the tube socket lug and clip it to lug 2 of the second preamp tube socket, the 12AX7.
You should be able to start isolating this buzz easily by eliminating stages of amplification.

Also.. who's and what input jacks are those and are you sure they are connected as switching jacks correctly?
Sometimes an ungrounded, unused input jack does all kinds of weird things to the preamp stages using the 1M fixed resistor as it's grid load.

[loudthud]

Do the input amd speaker jacks ground to the chassis? If so, the following should fix the problem.

Disconnect all input jacks and speaker jacks from the star ground. They should ground to the chassis.

Disconnect all connections from the pots to the star ground.

Disconnect points 1, 2 and 3 from the star ground. The Ceriatone layout shows that points 3 and 4 are connected on the backside of the board. You may have to remove that wire later (and connect point 4 to 5), but it's ok for now. Verify with an ohm meter that points 1, 2 and 3 are connected on the backside of the board. They should have no connection to the star ground at this time.

Connect point 1 to ground at the input jacks. It's ok to have a wire for each channel.

Connect all pot grounds to point 2. One wire for each channel.

The output transformer should ground at the speaker jacks.

[Bruce / Mission Amps]

Star grounds are GROSSLY over rated. And, in my opinion, this is one of those internet driven, "fantasy tech", silver bullets... which frequently DOES NOT WORK!
Mostly because it is not carried out to the ultimate end, which includes items such as lifting and isolating the input jacks from chassis ground... not sharing any audio ground paths with power supply filtering ground paths... etc

The main thing to do in a simple amp like this is:
make sure the 6.3v filament string is referenced to a DC voltage such as the power tubes cathode biasing resistor.
Also, keep the center tap of the power tranny high voltage winding, grounded at the negative lead of the first main filter cap, along with the screen node hi-v cap, and keep that part of the power supply grounding way over on one side opposite the input jacks. You can move the negative lead of the third filter cap closer to the preamp stage if you want... it will be very very slightly quieter if it is grounded closer to the preamp, but not much.
Then leave the input jacks self grounded right at the chassis and use a jumper wire from one grounded lug over to the grounding end of the cathode biasing resistor(s) of the first stage.
If this doesn't make a difference, you are chasing a red herring and have other issues.

Oops... ground the second preamp stage cathode resistor and pots to the same place the third filter cap is grounded as suggested by loudthud... although the volume pots can be ground to their shell if the third filter cap is also grounded to one of the shells.

[soundguruman]

Hi

I've just finished my second 5E3 build. I've put in the 6G3 tone circuit so that there's a separate tone and volume for each channel. Apart from that it's a stock circuit.

When I switch on there's a fairly loud buzz which is modified by the tone and volume controls.

I've disconnected the tone circuits and channel two leaving just the vol from channel 1 feeding pin 2 of V2.

The buzz remains, but disappears when the volume is around 8/10 - it returns when I turn it up full or below 8.

I've carefully checked all the wiring against the schematic and now I'm stuck - I don't know what to do next.

Could it be an earth problem?

Any advice would be greatly appreciated

Now that I look at the picture, it kinda looks like one of your 6.3V heater wires is grounded to the chassis lug.
(look after the pilot light)
In the old days, that's exactly how they did it. But not anymore. BOTH 6.3V heater wires should be off the chassis.
If you are looking at a very old original schematic, it may show the one heater wire grounded to the chassis. You want to change that.

[Jazz P Bass]

I do not see the heater to ground connection.
What I do see looks proper.
F1 & F2 with a grounded center tap.