HRDx to ODS Conversion... Help Please!!

[JazzGuitarGimp]

We can work through the bias supply changes shortly. First, I want to get an accurate understanding of the nomenclature. As Phil stated, the R and L designations are confusing at beat, But I have not looked at the schematic yet, so I am hoping this will become more clear once I do. I will check back in shortly.

Jason, if you can see the pin numbers on the bottom of the sockets, why don't we start out by stating what color the wire is at each pin, as I can see where they go at the other end. I realize not all pins will have a wire connected to them, some will have a resistor. So for those, if you can tell me the tube pin number and the value of the resistor connected to it. I don't mean to offend you, but I have no knowledge of your electronics know-how. So, if you do not know how to read the colored bands on the resistors, just tell me what the colors are from one end of the resistor to the other.

Thanks,
Lou

[JazzGuitarGimp]

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.

Hi Jason,

I am at a loss here. I do apologize. All of the resistors you've referenced (R1, R2, R7, and R8) are in the preamp circuit and have nothing to do with the output tubes. So I am guessing you are not referring to resistors. Likewise, L1 is an indicator in the switching power supply, and there is no L2 or L3 anywhere in the circuit. So, again, you must be referring to something else. Please help me understand what you are referring to.

I see you do have some wire colors mentioned. So let's start there.

ON THE LEFT TUBE:
Pin 1. I don't understand this one.
Pin 2 has a white wire on it. This should be connected to one side of your 6.3VAC heater string.
Pin 3 has a yellow wire on it. Is this the yellow wire that goes to terminal block P11, where it says V45 V7.5?
Pin 4 has a brown wire on it. Does this go to the Output Transformer?
Pin 5 has a red wire on it, Does this go to terminal block P11, where it says V4.4?
Pin 6 has a yellow wire on it. where does it go?
Pin 7 is open. This is the other heater connection. If there is nothing connected to it, the heater in that tube will not light up; is this the case?
Pin 8 has a white wire on it. Is this the white wire that is soldered to the top end of R8 on the board (the one we've been saying should not be there?)

ON THE RIGHT TUBE:
Pin 1 has a white wire on it. What is L2?
Pin 2 has a yellow wire on it. This should be connected to one side of your 6.3VAC heater string.
Pin 3 has a blue wire on it. Does this go to the Output Transformer?
Pin 4 has a red wire on it. Does this go to terminal block P11, where it says V7.4?
Pin 5 has a yellow wire on it. Does this connect to terminal block P11, where it says V5.5 V6.5 ?
Pin 7 has a green wire on it. This should be connected to the other side of your 6.3VAC heater string.
Pin 8. I don't understand this one.

We'll get you going. No worries...

Cheers,
Loui

[jinx1499]

Sorry, I was not specific enough L and R speak to left and right tube and their placement. i.e R2 = Right tube, second pin. In hindsight, I realize how that would cause confusion. If there is a better to describe which tube and what pin, I'm very interested to learn!

[pompeiisneaks]

Sorry, I was not specific enough L and R speak to left and right tube and their placement. i.e R2 = Right tube, second pin. In hindsight, I realize how that would cause confusion. If there is a better to describe which tube and what pin, I'm very interested to learn!

Generally, both tubes should be configured identically so you would only want to qualify if for some reason one tube was different. The tubes are in a push pull configuration and half of the signal from the PI goes to one tube, the other to the other, but the same pins are used etc. The fact that there are pins jumpered between tubes does seem really wrong, usually the only time you do that is in a quad of tubes, then the basic connections for grid, and ot would go to one tube and jumper to the other tube so each half is the same. If I'm now understanding it, they connected the white wire from the R60 over to the right tube pin 1 and then from there over to the left tube pin 2?

that seems REALLY wrong. They connected the white wire to the heater of one tube and the ground of another? that's very wrong very, very, very wrong

That should be removed asap.

also it sounds like you're saying the yellow wire connects to pin 3 of the left and 2 of the right? Also very very wrong. Again I think pictures still are needed.

You have the blue wire, one half of the OT connected to pin 3 of the right tube and the brown one connected to left tube pin 4? also wrong. They both should connect to the same pin on both tubes, one for each side (blue/brown are the output transformer's sides of the push pull pair, and

I think from a lot of this it's more likely the pin numbers got mixed up, or the amp would have done really bad things when you powered it up etc.

~Phil

[JazzGuitarGimp]

Hi Jason,

No worries. We use reference designators for electronic assemblies. So you will notice on the board, all resistors have a unique number near them starting with “R” followed by a number. For example R45, R66, etc. Likewise for capacitors; for example C47, C16, etc. inductors start with L, transformers start with T, transistors use Q. And vacuum tubes use V. When you see a reference designator prefix, followed by a number, followed by a decimal point, followed by another number, now you are seeing a pin number for a specific part. For example, V4.7 references pin 7 of tube V4. Traditionally, guitar amps’ tubes are numbered starting with the first preamp tube, and moving in a straight line to the other end of the chassis, where the power amp tubes are. So, for example, a blackface Deluxe Reverb, looking at the back of the amp, the first tube at the right end of the chassis is V1, and moving to the left is V2, V3, V4, V5, V6 (phase inverter tube) V7 & V8 (output tubes) and V9 (power supply rectifier tube).

In your amp, again starting at the left, is V1 (clean preamp tube), V2 (OD preamp tube), V3 (phase inverter tube) and V4 & V5 (output tubes).

Lou

[jinx1499]

It's definitely possible that some things got mixed up. As I may have mentioned, this is well beyond what I know electronically. When I got the board, I thought this was going to be a bit more "paint by numbers" esque and so I'm wildly confused on why the tech didn't just plug in the wires where they went in the terminals. It's also a bit frustrating because I took it to him with the faith that I would get back a functioning amp and now it sounds like it could have been pretty catastrophic if I hadn't reached out to the forums here. I am very grateful for the help. What would you guys suggest I do moving forward? Can I drain the caps and do the work with your guy's oversight?

[jinx1499]

Also, the only wires in the terminal block are two yellow and two red.


The yellow wires are in v4.5& v7.5 and also v5.5 &v6.5 but are not connected to their closest terminal. They are connected to the far ends of the opposite side, if that makes sense.
the red wires are connected to their closest respective terminals - v4.4 / v6.4

No other wires off the power tubes pins are plugged into the terminal block.

[JazzGuitarGimp]

It's definitely possible that some things got mixed up. As I may have mentioned, this is well beyond what I know electronically. When I got the board, I thought this was going to be a bit more "paint by numbers" esque and so I'm wildly confused on why the tech didn't just plug in the wires where they went in the terminals. It's also a bit frustrating because I took it to him with the faith that I would get back a functioning amp and now it sounds like it could have been pretty catastrophic if I hadn't reached out to the forums here. I am very grateful for the help. What would you guys suggest I do moving forward? Can I drain the caps and do the work with your guy's oversight?

Can you solder?

[xtian]

Here is a detail photo of the power tube sockets in my Rev A HRD conversion. Pins 1+8 (closest to camera) are tied together with one leg of the 1R bias sense resistors. The other two resistors on that left-hand socket are the 100R heater balancing resistors. In the background, you can just make out my 5K6 grid resistors connected to pins 5 and 6 of each socket. That leaves pins 3 (brown and blue wires) and pins 4 (red wires).

detail.jpg

[xtian]

You can find many more photos and a lot more detail in the original thread for the Rev A board: https://ampgarage.com/forum/viewtopic.php?f=8&t=31844

[jinx1499]

I can solder and populated the board before handing it over to the tech. The wires plugged into the block are the same, but the rest looks way different. I will use your pics and write up as a guide and see what can be sussed out. I should be able to report back today sometime.

[jinx1499]

Can someone tell me how to drain the filter caps so I can safely work on these pieces?

[pompeiisneaks]

1. Make sure you have the amp unplugged
2. make sure to keep your second hand in your pocket always
3 drain the caps safely:
The amp has balance/drain resistors on the power supply rail, but you can check and drain by checking the DC volts along the TP7/TP8/TP9/TP10/TP11 points. Then if you see high voltages still there, you can get a (200k or more) very large resistance and (10 or 20W) watt resistor, and a few alligator clips and clip one end of he resistor to chassis and carefully w/o touching bare metal, touching the other end to any of the above test points an re-testing the voltage.

This is one of the more dangerous parts of the process. I like to clip the alligator lead I touch to B+ to a wooden chopstick and then I can keep fingers far away from where I touch.

Re check those test points and as long as you get down to the sub 5 volts DC range you're good, the caps will look like the voltage is climbing, but that's just capacitance refill I think is the term. Large caps tend to 'recover' some charge after drained, but not a ton. it won't climb to a dangerous level.

Edit: typo, added a decent resistor value/wattage

~Phil

[JazzGuitarGimp]

The board has a bleed resistor at each capacitor. If you turn off the amp, unplug it, wait about a minute, then measure the DC voltage at each of the test points as Phil suggested, you should find that all voltages have fallen to safe levels. Phil suggests 5V, and that’s what I look for as well. Though it’s pretty conservative. I believe the point at which most people start to feel a tingle is about 42V.

[xtian]

Any voltage over ~20vDC will give a good SNAP if discharged across a low resistance path like a probe or screwdriver.