HRDx to ODS Conversion... Help Please!!

[xtian]

From the pictures, it looks like all three relays are plugged into their sockets backwards.

I can confirm that the relays are oriented properly--they match my Rev A build.

[pompeiisneaks]

Oh good to know, so the negative voltages were right. Sorry I don't know much about that part of the circuit and should have probably stayed silent there

I agree for sure that the unshielded wires on the overdrive pot are going to cause a lot of noise in the circuit and be quite problematic. I would also suggest keeping it on the chassis, it's not something you should need to ever change once you dial it in for the first time. Similar to the HRM stack there on the board, set it to your preference, and forget it.

Agreed xtian I just looked up the datasheet, the bar on the top is at the NO side of the relay, opposite the coil. They look installed correctly to me too.

~Phil

[jinx1499]

I flipped the relays around - still no switching

[jinx1499]

Alright, I will swap the relays back to the original position

[sluckey]

Always loved the base layout on these style relays. No way to plug it in wrong.

[JazzGuitarGimp]

Here is the Rev A schematic. First, that mod to R60 is totally wrong. Put that back to stock.

Schematic, HRD TO ODS, Rev A.pdf

Correct, there should not be a wire from the top end of R60 to anything.

[JazzGuitarGimp]

Yep, you called it...
When doing it right, I got 41.2 off of 1
2 measured 18.7
3 measure 18.6

Hi Jason,
These voltages should be as follows:

1 40-ish VAC
2 This is a NEGATIVE DC Voltage (with respect to Chassis GND), in the range of about 50 to 55 VDC
3 This is a POSITIVE DC Voltage (with respect to Chassis GND), in the range of about 16 to 19 VDC

I can see in your picture that there is no wire at the right end of J7 (LOGIC GND). This point must be connected to your main Chassis GND point. Without it, the switching power supply will not run, and subsequently, the relays won't energize.

But you should remove that white wire at R60 before you do anything else. I can't see what pin # on the output tube socket the other end of that wire is connected to. Can you tell me, please?

Cheers,
Lou

[jinx1499]

I added some pictures to the folder of the wire so you can see the whole thing. Here's the link:

https://drive.google.com/file/d/1Oho017 ... sp=sharing

Can anyone explain to me the concern with it?

[pompeiisneaks]

R60 is one of the two negative bias resistors. For some odd reason that mod is taking the negative bias away from where it should come from and pulling it from before pins 5 of each output tube, which means the negative bias is going to be completely wrong. Those 221k resistors need to be 'before' the lines that feed the grids of the power tubes. This is why that white wire and the jumper off to the other tube as well needs to be removed and instead the only wires that need to be connected to pin 5 are the ones coming off the screw terminals.

The other part that I really can't see from the picture is what pins the white and yellow wires connect to? That part is too dark. It really seems to me like if the yellow wires which come from the board's pin 5/grid connections are going to a different pin than the white ones. In which case it's even weirder... What pins are those connected to anyway?

Remove the white wire coming off of R60 and the jumper it seems to have between the two tubes. . Give the logic ground a connection to a ground and you'll likely have a working amp... or at least you'll fix the obvious issues and we can consider any next issues.

~Phil

[jinx1499]

Thank you for the explanation! Definitely helps makes sense of all this. I added some more pictures to the folder, if they still don't help, I will look for any specifics you may have.

With Lou's grounding directions, i got the relays running! It seems as though the amp is like 1/2 power though. Could that wire be contributing to that?

[pompeiisneaks]

Yes absolutely. they did mention twice to remove those before powering up again.

The problem is that likely it's providing a much higher negative bias to the tubes, which is making them run very cold. Which lowers output power/volume. Do you know how to calculate the bias on the power tubes and set it correctly?

It's a procedure that is very dangerous if you don't know how to do it. But basically those white wires seem to be bypassing two very important resistors in the amp that need to be in place.

You'll want to calculate that as soon as you fire up the amp to ensure you're not running it too hot.

~Phil

[JazzGuitarGimp]

Hi Jason,

Yes, that wire could be the reason you’re not getting full power. The new photo is too dark around the tube socket to see the pin numbers, which are embossed in the plastic right next to each terminal. Can you get a flashlight in there and read and report back with the pin numbers for each color of wire connected to the tube socket pins? Also, what are your output tubes (EL34, 6L6GC, etc)?

Thanks,
Lou

[jinx1499]

Alright, I think I got them.
Looking into the amplifier from the control panel inwards:

Left Tube:
1 - Resistor in series with R8, L3, R7 to ground (chassis and center of screw down terminal)
2 - White wire - connected to R1
3 - Yellow wire - connected with R2
- Resistor in series with R7, L1, R8 to ground (chassis and center of screw down terminal)
- connected to v1
4 - Brown wire - running under board
5 - Red wire - Running to screw down terminal
6 - Yellow wire - Running to screw down terminal
7 - Open
8 - White wire - connected to R7
- Connected to v1

Right Tube:
1 - White wire - connected to L2
2 - Yellow wire - connected to L3
- connected to Green wire running to PT
- connected to indicator light
3 - Blue wire - running under board
4 - Red wire - connected to screw down terminal
5 - Yellow wire - connected to screw down terminal
6 - open
7 - Green wire - connected to indicator and Green PT
- White wire connected to L8
- Resistor in series with L3, L1, R8 to ground (chassis and center of screw down terminal)
8 - Resistor in series with L3, L1, R7 to ground (chassis and center of screw down terminal)

If something needs more clarification, let me know.

[jinx1499]

Oh, and the tubes are EL34s. The tech said he tried 6L6s but they were biasing too hot.

[pompeiisneaks]

I'm pretty sure I got more confused than before by the nomenclature you're using.

R is resistor so R1, R3 etc means "resistor one on the schematic" and L is an inductor or L3 is "Inductor 3 on the schematic"

what do R and L mean in your explanation? Do they refer to pin numbers or something on the board?

I think it would make more sense to specify the pin number. The 8 pin tubes are easiest understood if you just refer to them as Pin 1, 2, 3, 4, 5, 6, 7, 8 etc.

As for the EL34 vs 6L6, there was a discussion about this in another thread but the design was for the 5881's that came with most of the amps, but to convert it to using 6L6's was just a required change to the bias circuit. Just bypassing it with the white wires was not a good way to get that done.

If you do want to use EL34's (and the OT isn't as optimal for those tubes, 6L6 or 5881's were the designed range for the OT). Then more bias changes would be needed to get the right bias.

Basically, you need to probably go back to either 6l6's or 5881's and then we can give you the right bias resistor(s) for that setup, If you need El34's it can be done too, but would perform more optimally with a different transformer. (I don't know the exact numbers for all/any tubes, but the datasheets I just pulled say that EL34's want about 3400ohms for the OT and 6L6's like about 5600 for two tubes. So basically there's going to be an offset for the OT to speaker for EL34's that makes the tubes perform outside their expected parameters.

~Phil