#124 Build Questions

[lgehrig4]

The half power switch either grounds the cathodes of two of the power tubes to the solder lugs between the left and right pairs of tubes sockets or takes each through a 10k resistor and then through a single LED to the nearest solder lug. If you’re not doing the 1/2 power switch, ground the cathodes through 1 Ohm 1 Watt resistors to the solder lugs between the left and right pairs of tubes. You can then run a wire from each cathode pin to a test jack for measuring DC voltage (numerically equivalent to current in Amps) to set the bias.

Thats a great suggestion. I think I have a few of those test jacks for the probe laying around. I'm surprised thats not part of the design given that the bias pot control is on the outside of the chassis.

[martin manning]

I don’t know what chassis you’re using, but if it was made for an ODS build it might already have holes for the test jacks.

[lgehrig4]

I don’t know what chassis you’re using, but if it was made for an ODS build it might already have holes for the test jacks.

I'm using the ODS chassis sold by Amplified Nation here. There are some random holes on top in between the pt sockets that I could probably work with.

[martin manning]

There are some random holes on top in between the pt sockets that I could probably work with.

Not random at all. They are there for bias rest jacks ;^)

[lgehrig4]

Looking at the ODS Rectifier/Bias Supply board diagram(from link below) I see there are two connections that need to be made to the 10K bias pot (lug 1 and lug 2). The layout ( from A Collection of #124 Information (Schematics, Layout, etc.) shows only one, and from what I understand of the schematic is shows only lug 1 as well.

1. Do I follow the eyelet board diagram and connect to lug 1 and lug 2?
2. If yes to one, do I still run the other bias wire to lug 2? The one that comes from the 220K resistor pair on the main board.


https://ampgarage.com/forum/viewtopic.p ... 08#p365408

Also, does anyone know where I can find a layout/diagram the for the T4 + ODS Relay/LED Supply without using a voltage regulator? My transformer is 12 VAC. I purchased it after looking at another builder's photos not realizing they were using 24V relays.

[martin manning]

Looking at the ODS Rectifier/Bias Supply board diagram(from link below) I see there are two connections that need to be made to the 10K bias pot (lug 1 and lug 2). The layout ( from A Collection of #124 Information (Schematics, Layout, etc.) shows only one, and from what I understand of the schematic is shows only lug 1 as well.

1. Do I follow the eyelet board diagram and connect to lug 1 and lug 2?

Yes.

If yes to one, do I still run the other bias wire to lug 2? The one that comes from the 220K resistor pair on the main board.

Yes.

See the second note in the ODS Eyelet Boards thread https://ampgarage.com/forum/viewtopic.p ... 08#p365408 referring to the 183 layout. The only difference is the later SN amps have an additional filter capacitor (located on the bias supply board) connected from lug 2 (the output of the bias supply) to ground.

Also, does anyone know where I can find a layout/diagram the for the T4 + ODS Relay/LED Supply without using a voltage regulator? My transformer is 12 VAC. I purchased it after looking at another builder's photos not realizing they were using 24V relays.

Feeding 12VAC into the full wave bridge rectifier on your relay supply board will produce raw DC voltage of around 17V. You need the regulator to drop that down to 12V for the relays. .

[lgehrig4]

Looking at the ODS Rectifier/Bias Supply board diagram(from link below) I see there are two connections that need to be made to the 10K bias pot (lug 1 and lug 2). The layout ( from A Collection of #124 Information (Schematics, Layout, etc.) shows only one, and from what I understand of the schematic is shows only lug 1 as well.

1. Do I follow the eyelet board diagram and connect to lug 1 and lug 2?

Yes.

If yes to one, do I still run the other bias wire to lug 2? The one that comes from the 220K resistor pair on the main board.

Yes.

See the second note in the ODS Eyelet Boards thread https://ampgarage.com/forum/viewtopic.p ... 08#p365408 referring to the 183 layout. The only difference is the later SN amps have an additional filter capacitor (located on the bias supply board) connected from lug 2 (the output of the bias supply) to ground.

Also, does anyone know where I can find a layout/diagram the for the T4 + ODS Relay/LED Supply without using a voltage regulator? My transformer is 12 VAC. I purchased it after looking at another builder's photos not realizing they were using 24V relays.

Feeding 12VAC into the full wave bridge rectifier on your relay supply board will produce raw DC voltage of around 17V. You need the regulator to drop that down to 12V for the relays. .

Thank you Martin! To me this sounds like I am all set then. This is my first build using relays/regulators/jfets so I am not too familiar with these. I think I misunderstood the information I was given earlier in this threads. What I understand now is that I can proceed in hooking this up according to the schematic/layout if I am using these?

Hammond 166F12B (photo)
Power Rating (VA) 3.6
Primary VAC 115V 60 Hz.
Secondary (RMS) VAC 12 C.T.

7812C regulator

OMRON g5V-2-H-DC12 12VDC

IMG_3359.jpg

[martin manning]

Yes all good.

[lgehrig4]

Yes all good.

You made my weekend!

The shipping costs for part were starting to creep up to the parts themselves:)

[lgehrig4]

I'm up to the relays now and the OD Relay - Ratio & Master Vol connections are the same for both the main layout and he universal eyelet layout, but the PAB Relay connections are different.


PAB Relay ( from https://ampgarage.com/forum/viewtopic.p ... 08#p365408 )
Com 1 Treble CCW
Com 2 Bass Wiper
NC 1 R/J Sw Pole (5n)
NC 2 R/J Sw Pole (100k)
NO 1 Not used
NO 2 Not used

22M 1/4W from NC 1 to Com 1,
and NC 2 to Com 2


PAB Relay (from the layout)
Com 1 R/J Sw Pole
Com 2 R/J Sw Pole
NC 1 Treble CCW
NC 2 Bass Wiper
NO 1 Not used
NO 2 Not used

22M 1/4W from Com 2 to NC 2


In addition to the swapping of treble/bass and R/J Sw Pole connections on the relay it seems, there are these other differences that I am unsure of.

1. I would use two 22M resistors for the universal design( I haven't come across any photos of this even when the same universal eyelet was used (one could be underneath though)
2. For the R/J Sw Pole (5n), the layout has two .01 in series.

Should I follow the universal layout? If so can I keep the two .01's in series or would it be advisable to get a 5n?

[martin manning]

I'm up to the relays now and the OD Relay - Ratio & Master Vol connections are the same for both the main layout and he universal eyelet layout, but the PAB Relay connections are different.

...but they are doing the same thing, Com and NC are just swapped.

PAB Relay (from https://ampgarage.com/forum/viewtopic.p ... 08#p365408)
Com 1 Treble CCW
Com 2 Bass Wiper
NC 1 R/J Sw Pole (5n)
NC 2 R/J Sw Pole (100k)
NO 1 Not used
NO 2 Not used

22M 1/4W from NC 1 to Com 1,
and NC 2 to Com 2


PAB Relay (from the layout)
Com 1 R/J Sw Pole
Com 2 R/J Sw Pole
NC 1 Treble CCW
NC 2 Bass Wiper
NO 1 Not used
NO 2 Not used

>> 22M located on the R/J Sw and Treble pot, but electrically NC1 to Com1
22M 1/4W from Com 2 to NC 2

In addition to the swapping of treble/bass and R/J Sw Pole connections on the relay it seems, there are these other differences that I am unsure of.

1. I would use two 22M resistors for the universal design( I haven't come across any photos of this even when the same universal eyelet was used (one could be underneath though)
2. For the R/J Sw Pole (5n), the layout has two .01 in series.

Should I follow the universal layout? If so can I keep the two .01's in series or would it be advisable to get a 5n?

2x 10n vs. 1x 5n doesn't make any difference. Here's a photo of my 124 with both 22M on the relay board.

[lgehrig4]

Thank you once again Martin!

[lgehrig4]

Everything is coming along nicely thanks to you Martin and others who have been sharing their knowledge!

While I wait for the last few parts I was thinking ahead and one of my concerns is the PI Trim pot. I could not find a 5K of the same style so I opted for a 10K(single turn upright). Now I am reading about how sensitive and important of an adjustment this is. Before this is complete would it benefit to change to a 5K (will look like crap but I'll make it fit ), use a resistor to bring it down to 5K, or just leave the 10K in?

[martin manning]

...I was thinking ahead and one of my concerns is the PI Trim pot. I could not find a 5K of the same style so I opted for a 10K(single turn upright).

Keep the 10k. You may well need it depending upon how closely matched the sections in the PI tube are.

[lgehrig4]

...I was thinking ahead and one of my concerns is the PI Trim pot. I could not find a 5K of the same style so I opted for a 10K(single turn upright).

Keep the 10k. You may well need it depending upon how closely matched the sections in the PI tube are.

Nice! I'm not too familiar with Dumble style amps so tuning this in is going to be as much of a challenge as building it

I had a Two Rock Emerald Pro once but that was almost 20yrs ago and I cannot remember much about it. Home players don't usually get to know their gear as intimately as gigging to recording musicians.