dorrisant wrote: ↑Tue Aug 13, 2019 9:51 pmThe safest way is with a ground jumper between the two jacks. Just in case one of the jacks would loosen from the chassis, you'd still have connection to the OT secondaries. If it were to become disconnected while pushing signal through it, your OT would be at risk. Just one short wire goes a long way towards peace of mind.
I would jumper the speaker jack sleeve lugs together to insure a solid connection to the extension jack (doesn't rely on the bushings), and that gives you a redundant connection to the chassis (two bushings instead of one). The OT secondary ground reference is needed to eliminate noise, and for the feedback voltage, but if you were to lose the chassis ground, that doesn't remove the load from the secondary, and so there is no danger to the OT.
Just wondering if it would be safer to besides jumpering the 2 speaker jacks together if one should add an extra lead to the power tubes ground?
I tend to do this now after I had an earthing issue with the speaker jacks on an anodised chassis. Can't do any harm
martin manning wrote: ↑Tue Aug 13, 2019 10:18 pm
I would jumper the speaker jack sleeve lugs together to insure a solid connection to the extension jack (doesn't rely on the bushings), and that gives you a redundant connection to the chassis (two bushings instead of one). The OT secondary ground reference is needed to eliminate noise, and for the feedback voltage, but if you were to lose the chassis ground, that doesn't remove the load from the secondary, and so there is no danger to the OT.
Just wondering if it would be safer to besides jumpering the 2 speaker jacks together if one should add an extra lead to the power tubes ground?
I tend to do this now after I had an earthing issue with the speaker jacks on an anodised chassis. Can't do any harm
Question about supply grounding, Dumble grounds the screen grids supply along with the Pi supply at the power tube ground and the large filter caps along with the power transformer ground.
Two rock does it differently, by grounding the screens along with the large filter caps at the power transformer ground and then they separately ground the PI supply at the fx loop ground (with is grounded locally at the chassis).
I have been doing like Dumble but wondering if there is a preferred approach
Bombacaototal wrote: ↑Wed Aug 21, 2019 4:54 pm
Question about supply grounding, Dumble grounds the screen grids supply along with the Pi supply at the power tube ground and the large filter caps along with the power transformer ground.
Two rock does it differently, by grounding the screens along with the large filter caps at the power transformer ground and then they separately ground the PI supply at the fx loop ground (with is grounded locally at the chassis).
I have been doing like Dumble but wondering if there is a preferred approach
If it ain't broke, don't fix it. The big concept here is that the higher the current driving the particular grounding node, the farther away it should be from the preamp side. The Anodes ground through to their own spot. The screens are lower current, and therefore do better grounded near the PI which is a medium current part of the amplifier, but not so high as the power tubes, and therefore 'better' BUT you can also ground as two rock did, either will work, but there's a slightly higher chance of introducing noise through the screens in a ground loop from the main power tube anode, I think this is why dumble separated them to the PI.
Bombacaototal wrote: ↑Wed Aug 21, 2019 4:54 pm
Question about supply grounding, Dumble grounds the screen grids supply along with the Pi supply at the power tube ground and the large filter caps along with the power transformer ground.
Two rock does it differently, by grounding the screens along with the large filter caps at the power transformer ground and then they separately ground the PI supply at the fx loop ground (with is grounded locally at the chassis).
I have been doing like Dumble but wondering if there is a preferred approach
If it ain't broke, don't fix it. The big concept here is that the higher the current driving the particular grounding node, the farther away it should be from the preamp side. The Anodes ground through to their own spot. The screens are lower current, and therefore do better grounded near the PI which is a medium current part of the amplifier, but not so high as the power tubes, and therefore 'better' BUT you can also ground as two rock did, either will work, but there's a slightly higher chance of introducing noise through the screens in a ground loop from the main power tube anode, I think this is why dumble separated them to the PI.
~Phil
Thanks a lot Phil, very clear and thanks for the explanation.
I managed to trace one of the issues I was having. There was a louder than expected hiss/hum, by grounding the point before 220k of the recovery triode the noise was still there, by grounding PIN 2 (I wired my recovery on the first triode) the noise was completely gone.
Another thing I noticed was grounding the point in between the 22M and the .05uF of the LNFB (mine is just one 22M and one .05uF) the noise was gone. I thought I had a failed component and replaced first the .05uF and made no difference, I then replaced the 22M and again no difference and lastly I replaced the 220K and yet again the same amount of noise.
Last attempt was trying a few tubes and also no difference.
The only possibility in my mind is a bad socket? But before I go into this bigger task does it sound indeed like a bad socket?
EDIT: replaced the socket and it is fixed. So either the socket or a cold solder joint
Bombacaototal wrote: ↑Sun May 12, 2019 7:01 pm
I am a bit puzzled about an issue I am having with the amp which I can by no means fix it.
Whenever I start the amp there is a lot of noise for the first 10 to 20 seconds, and then the noise stops until next time I turn the amp on. I made a recording which is attached.
Any idea of what may be the cause?
Revisiting this amp trying to sort the issues. I found out the cause of the issue mentioned above. I replaced the 6V6 power tubes and the weird noise at start up were gone.
Bombacaototal wrote: ↑Sat Aug 17, 2019 9:14 pm
Many thanks for the reply Gil, so when nothing is plugged to the input the jack is grounded to the pre-amp star ground, given they are isolated from the chassis with washers.
The master volume was fairly dimmed, around 3 o’clock. Power tubes are 6V6 from TAD and the grids are 3.3k. Let me experiment with the master while the squealing is happening. I will also experiment with the jacks on the FX loop.
The scope is a great idea as well, I need to get one sooner than later
I removed the jacks and soldered every thing again. Works perfectly now!
Bombacaototal wrote: ↑Tue Jun 18, 2019 1:05 pm
I will go back to the low plate skyline 124 soon and just wanted to double check something. The bass pot without the Rock/Jazz and without the relay is wired as follows: bass right lug connects with the treble left lug and 0.1uF on the board and there is a jumper from the middle lug to the right lug, correct?
Just for future reference, I dropped the jumper from the middle lug to the right lug to reduce the bass a bit and with this configuration the .01uF needs to connect to the right side lug in order for the .001uF across the bass pot to ground to make effect (filtering some of the bass out) and therefore the wire that goes to the treble pot needs to be in the middle lug.
Unrelated question but following the schematic below whereby 100K pot (voltage divider) is followed by a fixed 1M resistor, I am trying to understand what the pot is doing to the value of the 1M resistor.
They are not in parallel as the 1M is not going to ground, and obviously not in series. So is the relationship of the 1M resistor with the pot a voltage divider as well?
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without more context around it, my best guess is the 100k pot is a voltage divider like a tone/volume pot, and then the 1M is some form of grid stopper but does seem a bit high. It may be used to tame a pretty heavily gained amp before it hits the grid of the next tube? Again since there's nothing before and after it's a guess.
pompeiisneaks wrote: ↑Mon Sep 02, 2019 3:28 pm
without more context around it, my best guess is the 100k pot is a voltage divider like a tone/volume pot, and then the 1M is some form of grid stopper but does seem a bit high. It may be used to tame a pretty heavily gained amp before it hits the grid of the next tube? Again since there's nothing before and after it's a guess.
~Phil
Hi Phil, thanks for the reply.
I am trying to figure out if it is feasible to add a Fender reverb after the OD stage of an ODS, and therefore trying to understand the effect of the Ratio pot to the large resistor that Fender uses for the dry path (3.3M or 2.2M on the Hotel Hog). What I am trying to answer is if the 100KB pot will for example act as a parallel resistor and reduce the value of the large resistor (1M in my example) to 90K, making therefore this plan a bust.
