Hey Guys,
I recently completed a 5e3 with larger transformer for use with kt66s.
I have a hum now that I am not sure how to get rid of. if someone could have a look and see if they notice anything that I have missed or something I did wrong please let me know. or any help is greatly appreciated.
You used a different ground scheme than stock. Try grounding your input jacks to the chassis near the inputs. And or ground the entire preamp to the chassis front , leave the power supply grounded to the star lug near the PT.
Review the original layout for ground scheme. Also, noticed your output jacks are not grounded.
+1 on BillyZ's comments.
On V2, on the V1 side of it, it appears like there is a plate wire resting on the filament wire. Separate these. Check the rest of the amp for this sort of thing. I realize, pictures may be deceptive and it may actually be fine.
Hey thanks for the replies. I think I did it backwards as I have most of the other wires raised rather than the filament wires. They look touching in the photos but they are not really near each other at all. Is this still alright to do or should I switch it to the other way round? I will do it anyway just as practice I guess. I'll check all the grounding too.
This is my first build so I am still trying to learn as much as I can. Man is it addictive!!
I would make the changes as have been suggested, but I would only change things one at time. For instance, leave the heaters alone and change the grounding. Then take note of any improvements. Then change the heaters alone and take note. It may be obvious, but in this way, you will learn the impact of each change. Also, I didn't spot whether your heaters have a center tap or if you have created a 'false' one with resistors. If you don't have either then add the 'false' CT. I have found it helps quite a bit in 5E3 builds.
a_e_a wrote:I think I did it backwards as I have most of the other wires raised rather than the filament wires. They look touching in the photos but they are not really near each other at all. Is this still alright to do or should I switch it to the other way round? I will do it anyway just as practice I guess. I'll check all the grounding too.
Tucking the heater wires into the bottom/back crevice of the chassis is classic tweed era strategy. Clean up your grounding and you may be there.
Ok so I am not exactly sure which part the centre tap is. Haha. I really am trying to figure out what everything is but it is taking a while. Little help? I just did a search but only found people talking about whether a ct should be grounded or not.
Your center tap would be the 0 lead between the two 340 leads. The grey wire which you have grounded at the transformer lug. Pull your first two filter cap grounds and ground them here as well. If memory serves me from your second filter cap pair you have a ground running under the card to the first section of the preamp. This section of the preamp should not share it's ground in this manner with that cap pair. Better if you run a seperate. You really should follow the ground scheme from the schematic very closely with this type of amp. Most have problem,s when they stray from it.
Last edited by passfan on Thu May 05, 2011 11:26 pm, edited 1 time in total.
Ok so I fixed the grounding and some solder points. After resoldering pin 2 on v1 (first tube I hope that's right) there is still a hum when I touch it with the chopstick. I have also noticed that touching any of the pins I can hear it through the speaker. Does this mean the tube has gone microphonic and needs to be replaced? Could this also cause the hum?
There was no pop but a small buzz and every time I was touching any pin with the chopstick it was sounding like high pitched metal chinging. Only on the first tube not the others which is why I was worried.
I did ground the output jacks but it made no difference. I did work off the ceriatone layout rather than the original. (as this one is for a bigger transformer and 6l6 tubes). This may explain why I have grounded things a certain way.
Ok so the hum comes through even when the volume is off and the tone is up. Also comes through either channel. This would mean it's grounding in the preamp somewhere yes? Which 2 filter caps are the first two that were mentioned I should change? Sorry I am kind of understanding but not which specific ones. Are they the 22uf ones from the preamp tubes?
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