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Silverface Bandmaster Reverb
#1
The Bandmaster has been out of service for a long time, 25 years maybe? Retired, getting back into electronics. Working on the power supply. Wondering if anyone could suggest good suppliers of electronic parts ( caps, resistors ect), preferably in Canada.

Thanks
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#2
I usually source my stuff through Mouser (http://ca.mouser.com) or Next Gen Guitars (http://nextgenguitars.ca). Both offers free (and fast) shipping for orders over a certain amount and I only had good experience with both so far (ordered multiple times from each)
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#3
(01-20-2019, 06:12 PM)Vostre Roy Wrote: I usually source my stuff through Mouser (http://ca.mouser.com) or Next Gen Guitars (http://nextgenguitars.ca). Both offers free (and fast) shipping for orders over a certain amount and I only had good experience with both so far (ordered multiple times from each)

thanks a lot. really appreciate the feedback.
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#4
Hi Guys

Mouser (TX) and Digikey (MN) both offer free shipping to Canada for orders over $100cdn. You can place your order in CDN$ and they charge HST, so everything is taken care of and the shipment simply arrives at your door via Fedex or UPS. Mouser and Digikey both ship quickly and support the products they sell. You can get everything except tubes and tube sockets from them

For tube sockets, I buy these direct from China, which is where CE Distribution and everyone else gets them from. If you want a North American rep, CE is good, but Canadians will have to pay HST and a handling charge for the border bribe.

Within Canada, Electrosonic USED TO BE a  viable option. However, they have gone through some corporate changes and now behave quite unethically. Specifically, their site says online orders can get free shipping but when you try to place an order it is pending shipping charges. To make matters worse, they do a pre-authorisation on your CC of an amount much higher than what your order is for.  For example, I placed an online order with them that should have been about $303cdn. A couple of days later I get a call from them saying my card has been declined. I ask them how much they were trying to authorise and they say $553. I can't believe it !! They say the "extra" is to cover unexpected shipping charges despite the fct shipping should be free on my order, so I tell them to cancel the order right away.

I was also placing n order with another company and their transaction did not go through. I look at my online banking and find that Electrosonic has now charged an amount of $330 to my card - not the $303 of the original order - and this AFTER I've told them to cancel the order. I call my bank and tell them what went on; they call Electrosonic while I'm on the phone with them; the ES person claims to have reversed the charges long ago but the bank says they see the charge was only reversed a minute ago. Since I can hear their conversation, I can also talk to both parties and suggest that ES's action violate privacy laws within Canada, that they have no right to know how much money I have above the order amount.

Anyway, I strongly recommend AGAINST using Electrosonic.

A friend of mine had been telling me about the great deals and price matches he got with ES, which is why I tried them again after about a decade of not using them. After my experience, my friend called his sales rep to ask about the excess authorisation amounts and decided not to use them after that. A sales guy called me later to try to plead their case but being both a CC merchant and card holder I know both sides of the way things should be conducted and could not see how they could justify their position.

As an aside, the CC I use is called a "travel card". It is actually a gateway card parents are supposed to get their kids, so the kids get used to pulling out the CC. It is loaded from your account, so it is your money you spend NOT the banks - so technically it is not a credit card, more like a debit card that has a visa or mastercard number. Do not confuse it with a visa-debit or MC-debit card, which are what you can do your ATM stuiff with but it defaults to CC function elsewhere (online or purchases). My card won't help you build a credit rating but neither can you get into trouble with it. I put funds into it seconds before I use it.
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#5
Thanks a lot for your feedback, both the good reviews and the not so good. It's nice to have input on who to deal with and stay away from.

I have a question concerning the power supply cap replacement. The Bandmaster has 2 series connected 70 350v caps with 220k 1w bleeder resistors. It is exactly the same as Figure 3-13 in Principles of Power. I can't seem to find 70mfd 350v caps, thinking i will have to parallel the caps to get the rating. maybe i am just not very good at looking at the catalogues, but if I parallel them should I go a little higher, stiffer? Say, parallel a 47 with a 33? Are there other considerations for this connection using paralleled caps, and should I consider upgrading all the 1w resistors to 2w, the section on the series connected capacitors in POP suggests 2w.

Thanks...
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#6
Hi TiCatFan

Two 70uF caps in series provide an inadequate 35uF net capacitance. The operating voltage in this amp is likely 470V considering its vintage, and the series-caps have a net voltage rating of 700V. The turn-on surge is nowhere near 700V, nor is it likely over 500V, so it should be safe to use a single 500V to replace both of the stock caps.

I would use a snap-mount cap of 100uF - 500V and use a zip-tie to secure it. A modern cap with these ratings and a life of 10,000-hours is quite small compared to what is in the amp.

Some players and techs like the sound of series-connected caps as the ESR is higher then. If you prefer to go this route, even for purely aesthetic reasons of replacing two caps with two caps, then use 68uF or 82uF caps - or even a pair of 100uF - and wire them as you see in the amp.

Have you determined that the stock caps are actually bad? If they are working there is no need to replace them despite the fact they are way past 14-years old. A lot of techs change caps in amps simply because they don't know what else to do, it makes them money, and the customer feels okay with it because of all the misinformation he read on the web PLUS the customer understands what recapping is.
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#7
thank you for the response, it has helped me a lot. The Bandmaster is a 71 I believe, the filter caps look like they might be original. When i did a power up with only the rectifier tube in place I got some smoke, came from the filter cap tray. The cap at the PI node was leaking oil. The resistors sitting on top of this cap didn't look happy. Yes, I can change just this cap and the resistors, I can always change the other caps when/if they fail. I will learn a lot more by doing one thing at a time and observing the results. And that is the point, to learn.

According to the schematics, the standby on voltage from the rectifier is 440v, but the standby off voltage is 510v. This is what hits the first filter point, the series connected 70uF 350v caps.
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#8
Hi TiCatFan

Fender goofed with the standby wiring. First, it is a wonder this switch was ever included - see the article about standby switches on my site - the upshot is that standbys are potentially hazardous and they have little relevance in a guitar amp resulting in most people not using them "correctly" (a loaded word since the voltage is not high enough, the power is not high enough nor are the tubes expensive enough to justify adding the s/b). Second, the circuit position for the switch does not help switch life itself as it must make / break DC rather than AC. Really, the standby should be bypassed - shorted and use the switch for something else.

The only good thing Fender did with the s/b wiring was to add bleeder resistors across the main filter caps. These enforce voltage sharing, but they also discharge the caps after the amp is turned off. However, if you are inclined to USE the s/b as people suggest, the other caps in the amp might still have a charge when you open the amp. The best way to assure that all the caps are discharged is to bash on the guitar and turn off ONLY the power switch. The sound will fade down to nothing and the caps will be safe for you to poke around inside the chassis.

It sounds like this amp has not been used for a long time? You should never power an old amp like this directly with full mains voltage. Instead, use a Power Limiting Safety Socket (light bulbs) to limit power. First turn-on should be without power tubes, so you can verify that all the voltages are present ESPECIALLY that bias voltage is present right at the tube sockets.

Your amp seems to need a justifiable cap job.
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#9
I ordered some stuff from Mouser late one afternoon and it was delivered at noon the following day, these guys are good.

I definitely use the Power Limiting Safety Switch.

The 100 uF cap that I got to replace the series connected caps was too fat to fit into the filter cap tray. I had a 47uF that i installed. Replaced the rest of the filter caps, and the resistors around them. No more thunder, cracks and pops. Nice. The noise level is actually pretty good. Some solder connections in the amp I want to redo, and I might take a stab at galactic grounding.

When I was doing voltage checks, Plate and screen voltages on the 6L6s were 395, schematics put the plate at 437. they have the screen at 435 before the resistor. Can anyone tell me if the discrepancy in plate voltages is important and what it may indicate. The OT is only dropping it a couple volts, it is lower right from the rectifier. Should I try replacing the rectifier tube??

Any help would be greatly appreciated. Thanks...
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#10
Hi TiCatFan

I suppose we assume that you checked the voltages first without tubes and going through the PLSS ? Then tried tubes still through the limiter? Note that even with modest limiting from a pair of 150W lamps in parallel, all the voltages will be lower than stock. If you bypass the lamps the voltages will rise up a bit.

Simply changing the filter caps will not cause a reduction in voltage unless there is a bad connection, but then you would expect to see a drastic reduction and have quite a bit of hum.

The OT has no effect on screen voltage unless it is wired ultralinear. In that case, Vs is only a few volts lower than Va if at all and could actually be slightly higher depending on the DC resistance of the sections of the OT primary.

The solder connections in the amp are pretty large which gives them good longevity, but even so, after enough time they will become fragile and go cold. If you are careful, you can redo all the connections and eliminate that mode of nuisance or failure. To redo a connection, add fresh solder and use a Soldapult or similar to remove the solder with live heat. Then add fresh solder. Go to the next connection. Each connection should not take very long to do. Of course, you won't be able to remove all the solder from an eyelet or from around wire or component ends bent around the tube socket solder lugs - don't take the connections apart! - just remove the bulk solder and add fresh.

Also, when you go to sites like Mouser and Digikey, they have quite good search engines. For a given component type, there will be many parameters listed and as you refine the search by using the "Apply Filters, each updated search will show more and/or different parameters. I try to keep each segment of a search limited to two or three parameters - sometimes just a single parameter - especially if I will be searching for similar parts but say different values. This keeps the one search open to looking for the different values just by going back one step. In any case, the dimensions of the caps are often right there in the master search. Dimensions are often the make or break point for finding a replacement part or something to fit into a new build.
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#11
Another project that is currently in the "thinking stage", I am considering vertical mounting of one or more pcb cards. What i don't know is how to do this. are there brackets that can be used for this? Bend some metal and use standoffs? any suggestions? appreciate any help i could get on this...

thanks...
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#12
Hi TiCatFan

How you mount those boards depends on what will be on them. If it is just components, then right-angle brackets will do; Keystone has a dozen or more types - check them out at Digikey or Mouser.

If tubes will be on these cards then you need properly spaced brackets if it can only be secured along one edge. otherwise, if such a tube card can be placed along a vertical chassis plane then you would use standoffs or spacers as for horizontal mounting.

Daughter boards that are mounted on larger (mother) boards can be secured several ways that depend on whether the small board should be easily removed. You can use right-angle brackets or a sturdy connector interface. For example, on an old project I used 100mil connectors for electrical connections but a couple of 156mil single-pins to secure the card. The latter require 8-ounces of pulling force per pin to separate, so the little card was not going anywhere too easily. as the 156-family has very tight board-to-board connectors.
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#13
Thanks, I had spent a couple days looking up vertical PCB mounts and other such things and had gotten nowhere. My search skills are sadly lacking.

I have a question to do with nibblers? Don't want to spend lots of money on tools I may only use a few times. Can anyone give me any input on whether the cheaper nibblers function well or are just a waste of money? I have seen power nibblers which are just too pricey, drill attachments, and hand held plier style ones. I would appreciate any input as I have no experience using these.

Thanks.
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#14
Hi TiCat fan

When it comers to most tools, they usually pay for themselves in one use and a nibbler certainly does this easily.

The standard hand nibbler is plier-like and has  head with a movable tooth. You begin with a hole that is large enough to fit the head through, then nibble away metal to make the shape or size of hole you need. Do not try to bite off more metal than the tool can handle, so if it is thick material take small steps, same with if it is hard material - steel compared to alumunium. Stainless may be impossible with a hand nibbling tool.

Regarding the capacitor search:
--First select capacitors
--then (leaded) aluminium electrolytic
--once you are into the general field of aluminium cap selection, select 'in stock' and press 'apply filters'
--then select the voltage range suitable and 'apply filters'
--then select values you want and 'apply filters'
--then select 10,000-hours (1k-hr caps are junk); you could select 5,000 and up, then 'apply filters'

Hopefully you see enough range of caps to choose from.  You can click on any of the parameter columns to put the list into any order you wish, say by lowest price to highest, or skinniest to fattest. The initial list must have a sort reason but it has never seemed obvious to me.
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