Build Thread:PQD2

[miszt]

read up and answered my own question, never mind 400V's it is

 

[miszt]

I'm nearly ready to think about powering up, but I'm confused about the drop resistor for the 250V, I've got the suggested resistors from the BOM, but haven't put one in yet, what voltage am I supposed to be aiming for after the drop resistor?

(I'm using a 220V (secondary) transformer)

Argh also thought I had 0.5A on the 220V, but it is 0.05A :-/ is that enough for this?

 

[Gustav]

I'm nearly ready to think about powering up, but I'm confused about the drop resistor for the 250V, I've got the suggested resistors from the BOM, but haven't put one in yet, what voltage am I supposed to be aiming for after the drop resistor?

(I'm using a 220V (secondary) transformer)

Argh also thought I had 0.5A on the 220V, but it is 0.05A :-/ is that enough for this?

50mA is more than enough.

Aim for the 250V written on the silk screen after the drop resistor...(somewhat lower won't hurt. Dont go higher)

Gustav

 

[miszt]

I'm nearly ready to think about powering up, but I'm confused about the drop resistor for the 250V, I've got the suggested resistors from the BOM, but haven't put one in yet, what voltage am I supposed to be aiming for after the drop resistor?

(I'm using a 220V (secondary) transformer)

Argh also thought I had 0.5A on the 220V, but it is 0.05A :-/ is that enough for this?

50mA is more than enough.

Aim for the 250V written on the silk screen after the drop resistor...(somewhat lower won't hurt. Dont go higher)

Gustav

that's a relief thanks! took me ages just to find that transformer lol

still a bit confused, but i might have my calculations wrong...

230V AC to DC ~300V
then to 250V @ 0.025A (guess on the current?)

...gives me ~2K drop resistor?

which is why I'm confused by the 12-20K suggestion in the BOM

 

[Gustav]

i might have my calculations wrong...

Could be...In order to check, you could simply try, then measure the voltage drop using a value in the suggested range before replacing with your calculated value if needed...

Gustav

 

[miszt]

i might have my calculations wrong...

Could be...In order to check, you could simply try, then measure the voltage drop using a value in the suggested range before replacing with your calculated value if needed...

Gustav

I guess that's what I'll have to do, just don't like pulling those big resistors out, they seem to suck up allot of heat and I find i'm heating the pads far longer than i'd like; i'll see what voltage I actually get after the caps and see

Need to double check some of these caps that are hard to read on the board, have I got this right...

3.3nF (into A2)
15nF (into above cap)
2.2nF (into A3)
10nF (into above cap)
6.8nF (into A5)
3.3nF (into A6)


lastly, a couple of my inductors seem to be matched only within 10%, 4 of them about 2%, is there a recommended tolerance for them? i don't mind getting more and matching them, but i'm not sure how accurate the meter is for inductors, or how close they need to be anyway...

 

[Gustav]

have I got this right...

3.3nF (into A2)
15nF (into above cap)
2.2nF (into A3)
10nF (into above cap)
6.8nF (into A5)
3.3nF (into A6)

https://pcbgrinder.com/download/PQD2/PQD2-schem.pdf

i'm not sure how accurate the meter is

Me neither...

or how close they need to be anyway...

Me neither...

If you are matching caps to 10%, it would make sense to do the same for the inductors. If you matched your caps to 5%, if would make sense to do the same for the inductors, and if you matched your caps to 1%, it would make sense to do the same for the inductors.

Gustav

 

[miszt]

cant read the labels in the schematic either, for the caps going into A1-A3 (apart from the first 3.3nF)

 

[Gustav]

cant read the labels in the schematic either, for the caps going into A1-A3 (apart from the first 3.3nF)

3.3, 15, 2,2, 10.

They are in pairs of parallel, so they add up to about 18 and 12.

Gustav

 

[miszt]

great thanks!

i managed to find a reference to the current draw for g-pultec, 0.005A to 0.006A, which explains the 15K drop resistor (much prefer to work these things out, rather than experimenting lol)


also got a pair of <1% matched inductors from don-audio, so apart form the big 4.7uF cap after the audio transformers, everything is nicely matched ...except the tubes...

at the moment I have a pair of "vintage" tubes (siemens), matched fairly closely (110/104 and 108/102 - whatever that means?), but I'd like to get a pair of new-build tubes that are more closely matched, any recommendations? the only recommendations I've found so far are for vintage tubes, with mostly scathing reviews of new ones  but i'm sure Manley aren't using NOS in their kit...

 

[CiaoPatsy]

Hey Gustav, just placed an order for this.

I'm looking at the switch resistor value sheet. Is the column in blue the typical resistor values that can be dropped in and used?  Sorry if this has been asked. I'm not completely clear on this part of the build.

 

[miszt]

all the resistors marked blue in the spreadsheet are standard values, you can get them all on RS online - I did find that RS had a huge mark up on a few of the values, for eg the 1K resistors were something like £1.50 each lol you can get them on ebay for ~99p for 30-50; but most on RS where ~0.15p (still a bit over priced, but even tho they are standard values, many of them cant be found on ebay)

 

[Gustav]

Hey Gustav, just placed an order for this.

I'm looking at the switch resistor value sheet. Is the column in blue the typical resistor values that can be dropped in and used?  Sorry if this has been asked. I'm not completely clear on this part of the build.

Check the schematic - the resistors are introduced in series for each step, adding them up one by one. So, its just series resistance.

The blue column represents the value at each step rounded to E96. The only reason its E96 is because I searched Google for a rounding formula, couldn't find one for E24, and making it was a bit over my head.

Theres no real need to use the odd values within a few %, as long as they are identical on both channels, and as long as your total resistance on the switch adds up to the same total.

Gustav

 

[miszt]

doh managed to forget to flip from AC to DC on meter.  :-[

 

[Gustav]

Some how I am getting 700V after the drop resistor (15k)  :/ nothing smoked or exploded thank ****, not going to hold my breath over the tubes tho, I am confused as hell now, that means I need more like a 90K drop resistor, but, I feel like something must be wrong surely?

Was expecting something around 220V-230V...

1. What are the specs on your transformer?

If HV secondary is around 240, 700V suggest you may have wired 2x110V primaries (or a single 220/230 primary)  for 220/230V and powered it on a 110V outlet.

2. If your tubes are not running, the resistor won't do anything, since no current is being drawn, but before considering that further, make sure to wire the trafo correctly.

3. I know I am repeating myself, but wiring a trafo correctly is something best learned on low power projects. When you make a mistake like that and not be able to realise it after the fact, it suggests you are not going to be able to guarantee the safety of your own work, and in this case, that could be fatal.

So please, get someone local with the necessary experience to help you.

Gustav

 

[miszt]

(as edited above, I was reading with ac switched on meter lol all fine now, just need 20k resistor instead)

 

[miszt]

as I have said before, I have plenty of experience with mains voltage appliances, the transformer is not wired up incorrectly, there is no danger of me electrocuting myself or burning the house down! just a danger of me looking a bit silly because I forgot to flip from HV-DC to HV-AC on my meter


anyway...does the power/io board require the filter board to be attached in order to properly "experiment" with the drop resistor? because I am not actually getting much of a drop, its ~347V before the resistor, and 320~330V after (I've tried 15K and 20K), so I'm guessing that without a load from the filter board, i'm wasting my time until the filter board is attached?

still got a few parts on order for the filter board (the 3 pin Connector plugs/sockets arnt all the same size on the board, doh!), wondering if I can simulate it with a resistor across the connections for the filter board?

 

[Gustav]

I'm guessing that without a load from the filter board, i'm wasting my time until the filter board is attached?

No, the filter is passive, so it will not load your plate supply.

The tubes in the active make-up gain stage (both) need to be inserted and heater supply needs to be running - usually easy to verify by the glow, but its best to have a second meter giving you a heater voltage read-out.

LM317 can shut off due to thermal excess if its not properly cooled. We are drawing a lot of current, so its not uncommon in this project. This would cause you to lose the regulated heater supply.

IF that checks out, check voltage before and after the drop resistor, check the drop, calculate current draw, calculate needed drop resistor - or experiment with a larger value/resistors add up in series if you dont have them in larger values.

Gustav

 

[miszt]

hmm well, I was getting only 0.5V at the +/- of the diode bridge coming from the 9V AC, so I switched it out wondering if it might be faulty, but now I'm only getting 0.1V; wrong type of diode bridge perhaps? I thought the only difference between when was the amount of current they could handle...

0.0V @ 6.5V pad, unsurprisingly if nothing is making it thru the bridge

 

[Gustav]

hmm well, I was getting only 0.5V at the +/- of the diode bridge coming from the 9V AC, so I switched it out wondering if it might be faulty, but now I'm only getting 0.1V; wrong type of diode bridge perhaps? I thought the only difference between when was the amount of current they could handle...

0.0V @ 6.5V pad, unsurprisingly if nothing is making it thru the bridge

Set your meter to read DC after the bridge (the bridge "turns AC into DC"), and for reference, check the VAC on the heater input before the bridge.

Gustav