New 183 build

[gktamps]

Corona dope is used for arc protection.

[Charlie Wilson]

In #183 he painted the black paint or nail polish on the power tube grid resistors but why? I see it sometimes on the solder joints in the ac sections of some of his amps but I still can’t figure out why he did that and it seems random as to wether he does it or not.
CW

[jabguit]

Not sure what Mr.D used but I used this!. Home Depot carries it
LiquidTape_Rev_433x285.jpg
Tony

good for doping speakers, too.

cheers,

[Stephen1966]

Some time ago, I saw a guy on YT tearing down a laser targeting pod from a Tornado and when he pulled out the boards, they had a thick coating of what looked like epoxy. For mechanical strength, no doubt, but also I think for dielectric isolation. My wallet likes the idea of using nail varnish (hot pink or otherwise) but I can imagine how it's going to go when I stand in front of the perky sales assistant at the local cosmetics outlet and ask: "So, does this offer isolation from arcing and corona effects?... Will it protect from humidity and corrosion?... What about its dielectric strength?" I will be barred for life, I think

The Corona Dope seems to be the stuff to use. Being lacquer based, it is probably okay to remove and resolder any joints with just a hot iron and a bit of IPA. The Liquid Tape (Electrical - not the glue) appears to form a rubbery compound which will work, for sure, but I imagine cleaning it off would be a labour of love if the connection needed remaking. There is also something called 'Super Corona Dope' but nearly all of this stuff is shipping from the States - if they will ship at all. Reading the warning on the label it reads like a Doomsday prophecy... you will probably get cancer, your bollocks will drop off and your unborn kid will be deformed. I almost want it more now

On the other hand, there are plenty of PCB lacquers to go round over here, and - given the low risk of arcing anyway - it would probably be enough to apply a few drops of that to any high energy connections that share a small space with other conductors. Really don't know why the grid resistors would need it, there can't be much mechanical strength to a layer of lacquer and the risk of corrosion isn't something I would be worried about. Maybe MrD was applying it because the amps would need galvanic isolation from sea air [edit; looks like hammerite on the bottom of the chassis, but could it be zinc, or zinc based? Aluminium also makes for a good sacrifical anode]... if the amps were heading to the coast, but pure speculation.

Hot pink is good.

[Stephen1966]

First layout I have to construct is for the power supply.

I've been studying Tony's layout (which still seems the most reliable to me) the schematic by jasysg and the photos. They are all different. The odd one out here though, is the schematic which shows the standby switch before the reservoir caps.

This is from the layout:

Tony's PS layout.jpg

This, with the standby switch after the reservoir caps seems the most conventional and the photos of the 183 seem to support this as well.

I was reading Blencowe's article about power supplies and switching where he pours scorn on the idea of standby switches as having no real purpose in modern amps: http://www.valvewizard.co.uk/standby.html However many of the major manufacturers still use them and as a mute it has its uses. The argument goes that it shortens tubes life and puts a heavy DC strain on the switch itself but the switch is high amp anyway, and the only real issue - cathode poisoning - is likely to be a rare occurrence, given the average between parts of a set might be only 20-30 minutes and no-one in their right mind wants to leave their amps on standby for hours at a time.

Without a standby switch, if you take a break, you have to either have another switch which kills the signal early in the chain, or you have to dial your volume down, upsetting any previously adjusted levels you might have set. I'm going to include one - I think the pros outweigh the cons but what do you guys think?

[bepone]

I was reading Blencowe's article about power supplies and switching where he pours scorn on the idea of standby switches as having no real purpose in modern amps: http://www.valvewizard.co.uk/standby.html

i strongly disagree from many reasons, Blencowe just wanted to "be smart" with that..

[WhopperPlate]

I was reading Blencowe's article about power supplies and switching where he pours scorn on the idea of standby switches as having no real purpose in modern amps: http://www.valvewizard.co.uk/standby.html

i strongly disagree from many reasons, Blencowe just wanted to "be smart" with that..

Let’s discuss further! ! What about his argument specifically do you contest and why ? Besides trying to be smart

I have heard so many tech tales over the years on what’s proper, and I love to cross reference.

[bepone]

Let’s discuss further! ! What about his argument specifically do you contest and why ? Besides trying to be smart

I have heard so many tech tales over the years on what’s proper, and I love to cross reference.

lets discuss lets discuss..lets take first, practical.
what is the voltage in powering on without standby on all the electrolytic caps=?
it is maximum unloaded DC rectifier voltage, so in amps loaded per example if is 430V, this will be over 450V.
if the amp is working at 470V, on all the nodes will be over 500V!
it is very simple error in statement which with time can create problem with elcos, because i'm sure that in preamp section nobody using 500V electrolytics, more likely optimised, 400V or 450V... me first. also with the coupling caps is the same.. there are many on 400V. anode without tube conductiong will be at full DC voltage, coupling cap charged to max.
do we have also sand devices in the circuit ? will they survive?
so it is not even ok to mention this theory, or spread on the internet, because on the world existing at least 100.000 amps which can have problem with that...so actuallly Wizard is reducing the life of equipment with this statement. and he thinks that is opposite.

[Stephen1966]

Let’s discuss further! ! What about his argument specifically do you contest and why ? Besides trying to be smart

I have heard so many tech tales over the years on what’s proper, and I love to cross reference.

lets discuss lets discuss..lets take first, practical.
what is the voltage in powering on without standby on all the electrolytic caps=?
it is maximum unloaded DC rectifier voltage, so in amps loaded per example if is 430V, this will be over 450V.
if the amp is working at 470V, on all the nodes will be over 500V!
it is very simple error in statement which with time can create problem with elcos, because i'm sure that in preamp section nobody using 500V electrolytics, more likely optimised, 400V or 450V... me first. also with the coupling caps is the same.. there are many on 400V. anode without tube conductiong will be at full DC voltage, coupling cap charged to max.
do we have also sand devices in the circuit ? will they survive?
so it is not even ok to mention this theory, or spread on the internet, because on the world existing at least 100.000 amps which can have problem with that...so actuallly Wizard is reducing the life of equipment with this statement. and he thinks that is opposite.

Let's be clear, Blencowe isn't alone in thinking a standby switch is unnecessary. I don't think he was trying to be "smart". I do think the issues (cons) he pointed to were not really convincing enough for me to go along with his different way of thinking about these things.

It's interesting what you say about the start up though and this is where I have a problem with this power scheme

jaysg 183 PS.jpg

In the schematic by jaysg, the stby is placed before the reservoir caps, this would have exactly the same effect of unleashing the full rectifier voltage across all the caps, simultaneously. [Edit: the 2W dropping resistors would attenuate the voltages slightly but with no current yet flowing in the tubes the voltages would be high, point being this would be largely unfiltered voltages, with a large ripple current] I don't believe this is correct.

Looking at the photo of the original 183 the stby switch appears to be placed after the big reservoir caps. The line into the stby switch seems to come from the left of the board, where it shares the same eyelet as the rectifier line but the line out of the switch (R/Y) goes back to the board and shares a row of three connected eyelets which I assume, include the choke and the B+ to the OT.

-2473600415237578966.jpg

In the first stage of jaysg's schematic however, the PS has two 385V rated caps in series giving 770V handling (nowadays - interesting side note - it's easier to find 330u caps rated for 400V or higher), the next stage, two 350V rated caps giving 700V and the remaining three sections with pairs of 250V caps giving 500V each. So even without the switch, it would probably still be okay and given the time it takes for these caps to fully charge and settle down is probably less than a couple of seconds, a little bit longer for the rest of the circuit, then the voltage stresses are likely not long enough in duration to have any adverse or long-term effects on the caps. If the surge at power on was in the kV range, we might have reason to be worried. Like you though, I don't think it's a good idea to leave out the switch, and I would go further by saying we shouldn't negate its effect by placing it before the reservoir caps. Instead, it should be like Tony's layout, or as the photo seems to indicate.

[bepone]

yes it is ok in particular Dumble amp, 183, all elcos are in series, but statement is general and valid for all other amps in the universe. Dumble 183 is rare plant to have all supply nodes made from 2 elkos in series

[ijedouglas]

In the schematic by jaysg, the stby is placed before the reservoir caps, this would have exactly the same effect of unleashing the full rectifier voltage across all the caps, simultaneously. [Edit: the 2W dropping resistors would attenuate the voltages slightly but with no current yet flowing in the tubes the voltages would be high, point being this would be largely unfiltered voltages, with a large ripple current] I don't believe this is correct.

Looking at the photo of the original 183 the stby switch appears to be placed after the big reservoir caps. The line into the stby switch seems to come from the left of the board, where it shares the same eyelet as the rectifier line but the line out of the switch (R/Y) goes back to the board and shares a row of three connected eyelets which I assume, include the choke and the B+ to the OT.

I can confirm that in all the real Dumbles I have had a look inside, the standby switch is placed after the reservoir caps.

[neskor]

[Stephen1966]

In the schematic by jaysg, the stby is placed before the reservoir caps, this would have exactly the same effect of unleashing the full rectifier voltage across all the caps, simultaneously. [Edit: the 2W dropping resistors would attenuate the voltages slightly but with no current yet flowing in the tubes the voltages would be high, point being this would be largely unfiltered voltages, with a large ripple current] I don't believe this is correct.

Looking at the photo of the original 183 the stby switch appears to be placed after the big reservoir caps. The line into the stby switch seems to come from the left of the board, where it shares the same eyelet as the rectifier line but the line out of the switch (R/Y) goes back to the board and shares a row of three connected eyelets which I assume, include the choke and the B+ to the OT.

I can confirm that in all the real Dumbles I have had a look inside, the standby switch is placed after the reservoir caps.

Many thanks Ian, it's good to have this confirmed. I'm pretty sure the 183 (original) does this as well but there is only so much information you can get from a single photo.

Does anyone have any more photos of the 183?

[pompeiisneaks]

Oh please, there is a TON of proof that standby switches 'can' be implemented and not harm an amp, but they are NEVER needed unless you're running tubes that operate well over 1000VDC. Tube Guitar Amplifiers never do.

This is science, fact, proven and hashed out over and over. If you MUST install a standby switch be very sure you implement it well so you don't damage the amp. It's just better to never use them. I haven't used one in an amp ever since I learned the facts about why standby switches were used and in what cases. Leo Fender didn't understand this so he put them on amps and now everyone invents reasons as to why they 'need' them that are just false history.

~Phil

[Stephen1966]

I love Bob's videos, he's such a pragmatist. Haha, "...the world will always need bartenders"