|
|
Post by 2600 on Dec 31, 2018 16:10:55 GMT -5
You would think that after 44 years I would have learned all the tricks to fix design quirks in a radio like the original "VOX" Tram D201. Not quite. Even after all 20 electrolytic capacitors have been replaced there is an annoying 120-Hz "hum" in the receiver speaker, even with the volume control turned all the way down. Now, most users of this radio don't turn the volume control to zero, so I have largely ignored it all these years. With the volume turned up, and the channel noise it's not that noticeable. But now I need to sell this radio, and that hum annoyed me. Seemed a little louder than normal for this model, to boot. After a bit of head-scratching, I found that the chassis-ground connection on the volume/tone control was the culprit.  I cut the fat bare wire between the contol and a chassis ground lug and ran a gator lead to a ground lug alongside the 12AX7 volume-control preamp/squelch tube V402.  BINGO! There is still a bit of 60-Hz 'buzz' sound if you put your ear up to the speaker, but this was a big improvement. At a distance of a couple of feet, no more 120-Hz hum. No need for a pic of the final version, a wire soldered to the volume-control ground at one end, and to the ground lug at the other. Just goes to show that there's always a new trick to be learned, no matter how old a dog you are. 73 |
|
|
|
Post by tubefan on Dec 31, 2018 17:15:38 GMT -5
Way to go. Never stop learning. If you think you know it all you will soon be let down. Thanks for posting for the rest of us to see and try.
|
|
Sandbagger
Administrator/The Boss 
Posts: 6,247 
|
Post by Sandbagger on Jan 1, 2019 9:42:39 GMT -5
You would think that after 44 years I would have learned all the tricks to fix design quirks in a radio like the original "VOX" Tram D201. Not quite. Even after all 20 electrolytic capacitors have been replaced there is an annoying 120-Hz "hum" in the receiver speaker, even with the volume control turned all the way down. Now, most users of this radio don't turn the volume control to zero, so I have largely ignored it all these years. With the volume turned up, and the channel noise it's not that noticeable. But now I need to sell this radio, and that hum annoyed me. Seemed a little louder than normal for this model, to boot. After a bit of head-scratching, I found that the chassis-ground connection on the volume/tone control was the culprit. I cut the fat bare wire between the contol and a chassis ground lug and ran a gator lead to a ground lug alongside the 12AX7 volume-control preamp/squelch tube V402. BINGO! There is still a bit of 60-Hz 'buzz' sound if you put your ear up to the speaker, but this was a big improvement. At a distance of a couple of feet, no more 120-Hz hum. No need for a pic of the final version, a wire soldered to the volume-control ground at one end, and to the ground lug at the other. Just goes to show that there's always a new trick to be learned, no matter how old a dog you are. 73 Interesting. I have a similar low level hum on my D201, and a slightly worse one on my Titan. Not cap related, but I'll have to give this a look-see. I did notice that a couple of disk caps near the volume control are microphonic and I had thought that maybe they were coupling AC into the audio chain. But ground loops can certainly cause similar issues...... Thanks for the tip. |
|
|
|
Post by SIX-SHOOTER on Jan 1, 2019 13:36:09 GMT -5
Well one day when I am bored I will give this a try on my D201A which has the same issue as does my DAK X. Neither is very loud but I know it's there even being 50% Deaf in both ears I hear it.Thanks for the heads up.
SIX-SHOOTER
|
|
|
|
Post by 2600 on Jan 1, 2019 18:30:34 GMT -5
I haven't investigated this fault for the circuit-board D201 radios, only the original "hand-wire", or VOX version in the pictures.
When I get the chance, I'll post pics if we work out this fix for the circuit-board models.
73
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jan 1, 2019 21:53:13 GMT -5
I haven't investigated this fault for the circuit-board D201 radios, only the original "hand-wire", or VOX version in the pictures. When I get the chance, I'll post pics if we work out this fix for the circuit-board models. 73 Well, as they say, nothing ventured, nothing gained....... |
|
|
|
Post by 2600 on Jan 1, 2019 23:56:32 GMT -5
If you try it before I can, please report back. Makes me wonder whether the best alternative-ground point will be on the receiver circuit board, or on the RA board, the one that plugs in behind the VFO.
One or the other, probably.
73
|
|
Sandbagger
Administrator/The Boss
Posts: 6,247
|
Post by Sandbagger on Jan 2, 2019 8:57:30 GMT -5
If you try it before I can, please report back. Makes me wonder whether the best alternative-ground point will be on the receiver circuit board, or on the RA board, the one that plugs in behind the VFO. One or the other, probably. 73 That's the thing about ground loops. They're not always predictable. Trial and error seems to be the method of choice. When I get a little time, I'll pop the bottom cover off of the D201 and play in the sandbox....... |
|
Bradley
Mudduck
On air ch 32 am ch 36 lsb Wed and Thur 8:00 pm with Tram D201 Rats nest vox one too! and D201a
Posts: 9
|
Post by Bradley on Dec 17, 2019 17:24:28 GMT -5
Well one day when I am bored I will give this a try on my D201A which has the same issue as does my DAK MKV. Neither is very loud but I know it's there even being 50% Deaf in both ears I hear it. Thanks for the heads up. SIX-SHOOTER Hi Guys, I've had this problem as well on my D201 VOX Rats Nest, well i got adventurous and tried this trick of 2600's and it did work! it turns out the Tram folks ran a shielded line for the transformer a/c line to on off switch and grounded it back near the transformer chassis ground as well as at the ground lug for the volume chassis ground. well this is going to cause an induction from the a/c switch lines to the shield and bleed into the volume control connection at its ground point. so i did the change slightly different. i found a ground lug direct to chassis near the spot of 2600's that had nothing else on it and changed it. then i saw the shield ground. seeing that grounding at both points was redundant and clipped the shield at the volume chassis ground and taped it off. i know i probably didn't need to change the volume ground point but didn't realize till after the mod was done. then i didn't have to move the RTC control caps from that chassis ground . i still have a slight hum when the RTC control is CCW and strangely is squelched out when you set the squelch, gonna work on this one. I've noticed that the way they did the filament wiring in the D201A's is different to maybe solve the hum problem. also the speaker wires are not run with shielded lines so I'm gonna change those out too. Bradley Ch 32 am Lakes region Central New Hampshire currently living about 7 miles from winnisquam factory location |
|
Bradley
Mudduck
On air ch 32 am ch 36 lsb Wed and Thur 8:00 pm with Tram D201 Rats nest vox one too! and D201a
Posts: 9
|
Post by Bradley on Dec 20, 2019 12:42:23 GMT -5
Hi Guys,
back again for an update on the Counter clockwise RTC hum after i did 2600s mod, today i noticed that there was a J J manufactured tube in the V603 position KT 77 (Correction it was manufactured in Slovak Republic ) it crosses with the 6L6s in guitar amps so i had a G.T. (Groove Tube) 6L6 gt also a guitar tube i had which i had double checked with a Friends tube tester as good. I changed it out and BINGO! RTC hum gone! beautiful sound! on AM and SSB wholesome sound. there is still that very low level hum faintly like 2600 said if you put your ear up to the speaker which is inherent in the D201s. i wish to say thanks to 2600 for the help and the rest of the guys here that pass on info.
also got an idea to put a audio filter transformer at speaker im guessing 1:1? to see if it eliminates low level hum. any ideas?
thanks
Bradley
|
|
