Welcome, Guest. Please login or register.

February 25, 2020, 12:12:13 AM

Login with username, password and session length

Recent Posts

Author Topic: peavey roadmaster super duper festival  (Read 8059 times)

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
peavey roadmaster super duper festival
« on: April 03, 2015, 02:38:34 AM »
this amp is huge and cumbersome and a pain to take apart but i think its *mostly* working

i didnt do a road test but just took some measurements for now -

just a few questions (refer to attached schematic):

1) i get +300V at the PI supply, but on the transistor end of the load resistors i get ~10V everywhere i meausure - any of the transistor leads that arent at ground give me about 10.25V. one or more of the transistors bad probably? ive dealt with and fixed a bunch of these hybrid peaveys and almost ALWAYS the PI transistors have to be replaced.....

2) im getting a weird looking ripple at all points on the amp when measured with my scope. kind of a large, jagged wave. even when i touch the scope to ground its there. about 100Vp-p!! what the....??? i thought it may have been death cap related so i removed those caps but that only seemed to make it worse......any ideas?

3) related to that, what do the two caps on the power cord side of the PT actually do?


DrGonz78

  • Legendary
  • ******
  • Posts: 556
  • Chip Points: 69
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #1 on: April 03, 2015, 05:03:09 AM »
Well to help answer question 3, those are the X and Y capacitors. The x cap will go across the positive and neutral lines to help reduce differential noises from the power supply. The x cap if shorted will not pose a risk of shock onto the chassis but will short circuit blowing the fuse. Hopefully the guitarist does not have a foil wrapped fuse or something that will increase the chance of fire dangers.

The Y cap is your death cap as it's known in many circles. Of course if it goes leaky or shorts it presents a shock hazard. Since this amp was designed with a grounded plug it is obvious that they were really working to reduce noises from the mains power supply. You could always leave the X cap in to help reduce differential noises. You can remove the Y cap, but it might increase the ground hum noise of the amp overall.

You know after writing out my post I noticed a great thread on MEF about this very type of Peavey circuit.
http://music-electronics-forum.com/t14768/

Kinda of an interesting read at the end of the day. I remember running into my first X cap in an old Silvertone amp and it had the death cap too. I ended up installing a 3 prong and removing the Y cap. I left the X cap in the amp as the part was in good working condition and did not pose a shock risk to the player.

Edit: Also wanted to note that when I am mentioning this X cap on an old Silvertone I am probably wrong to call it a X cap. Anyone know better? From what I have read is that these X caps were named that way later on down the line from the older amps. Typically speaking Y caps can replace X rated caps but not the other way around. So my Silvertone had a Y rated type cap in the X cap position. I think that is right but someone here will know better I am sure. Also the history of all this stuff is way beyond my understanding too.
« Last Edit: April 03, 2015, 05:20:28 AM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein

g1

  • Legendary
  • ******
  • Posts: 632
  • Chip Points: 75
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #2 on: April 03, 2015, 02:57:21 PM »
It is best not to use the terms class X and type Y when referring to positions or functions.
What classX and classY denote is that they are specific caps approved for those positions.
ClassX is for line to line, classY is for line to ground. (neutral here is considered line, chassis is ground)
For example, a cap going from line to ground (what we call "death cap") is not class Y unless we specifically buy an approved "class Y" cap to use in that position.

http://www.justradios.com/safetytips.html
« Last Edit: April 03, 2015, 02:59:58 PM by g1 »

DrGonz78

  • Legendary
  • ******
  • Posts: 556
  • Chip Points: 69
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #3 on: April 03, 2015, 05:10:34 PM »
Thanks G1 I definitely see where my explanation was not the best as far terms etc. I understand this way better now thanks.  :dbtu: Sorry to derail the thread but I have to ask... Are these class X and Y the types of caps in this Roadmaster amp? I have come across these caps before and had only a vague understanding of their functions. Funny though that after reading your post I typed a google search for line suppressor cap and my first click to a link was the exact link you provided. That link you provided explains every question I have regarding the whole matter, very interesting. Plus I was reading the Vishay data sheets on class x/y capacitors last night so that helped too. Good info indeed thanks.

Also, in IIyaa's case does it sound like a component is shorted and the ground reference is not working in the circuit correctly? Perhaps what he is seeing is that term "Ghost voltages".

Edit: When I say "Ghost Voltages" I am referring to measuring voltages to ground and the ground would not be currently a valid point of reference anymore. Also, perhaps measure across or between components would give a more direct way to know what voltage is in a certain area of the circuit, if the ground path has become questionable.
« Last Edit: April 03, 2015, 05:27:44 PM by DrGonz78 »
“A person who never made a mistake never tried anything new.” -Albert Einstein

Enzo

  • Legendary
  • ******
  • Posts: 1899
  • Chip Points: 198
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #4 on: April 03, 2015, 07:27:09 PM »
If scoping the ground yields 100v, then that ground isn't, well, grounded.

The short answer to #3 is they reduce noise.

10v all over?  What is on the collectors of the 4249 level shifter transistors?  Ought to be zero, as they are grounded.

g1

  • Legendary
  • ******
  • Posts: 632
  • Chip Points: 75
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #5 on: April 04, 2015, 04:01:53 PM »
Are these class X and Y the types of caps in this Roadmaster amp? I have come across these caps before and had only a vague understanding of their functions.
No, these are DVL type caps (double layer?).  That was what was spec'd prior to classx&y for safety purposes (after it was realized caps used as "death caps" needed to be special). 
If this amp were being built today, they would have to use a classX for C59 position, and a classY for C60 position.  C60 is what would be considered the traditional "death cap" position.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #6 on: April 04, 2015, 07:21:46 PM »
on a separate note, i did some snooping around the PI and found that:

its clear from the underside of the board that the driver transistors were replaced - they are MJE 3439 - which seems like a suitable replacement BUT whoever put them in did not orient the b/c/e terminals correctly - i did some tests with the DMM on diode range and they have the base and the collector switched. probably took a guess and guessed wrong!! so no wonder the voltage is bad. im assuming they are probably fried because of that error? i found some replacements at the electronics shop near me so ill get those and put them in and see if the voltages look better -


Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: peavey roadmaster super duper festival
« Reply #7 on: April 05, 2015, 04:06:37 AM »
on a separate note, i did some snooping around the PI and found that:

its clear from the underside of the board that the driver transistors were replaced - they are MJE 3439 - which seems like a suitable replacement BUT whoever put them in did not orient the b/c/e terminals correctly - i did some tests with the DMM on diode range and they have the base and the collector switched. probably took a guess and guessed wrong!! so no wonder the voltage is bad. im assuming they are probably fried because of that error? i found some replacements at the electronics shop near me so ill get those and put them in and see if the voltages look better -



Well +1 for spotting the previous repair, and another +1 for realising and proving it was botched.   :dbtu:

Safer to assume they are dead, you don't know what else has happened to them (in the light of putting them in the wrong way).

{moral:  Your gear, and you can take a punt and it will be on your own head; client gear, where your client may end up looking like a doofus mid-song with a smoking amp, requires a higher standard (lest your rep end up smoking as well - your rep is your business card, to the individual tech it should be everything.  A good rep will feed you and maybe make you rich, but a bad rep can get you famous in the worst possible way).  They don't know and trust you to do it right, and by doing it right you build trust and good word of mouth, and that's priceless.}


Through a glass darkly, you seem to be gaining ground ilyaa.   :dbtu:

BTW, may I ask where you live?
If you say theory and practice don't agree you haven't applied enough theory.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #8 on: April 09, 2015, 02:36:47 AM »
thanks, Roly!

i live East of San Francisco -

i replaced the PI drivers and the voltages look better, but they are not balanced. one of the driver's collectors gives me 170V (the one hooked to the 100k resistor) and the other one (to the 82k) closer to 270V. the bases are at 10ish volts and the emitters are about 0.6V below that so thats okay. i thought the different collector resistors were there to balance the voltages out - the ~100V difference seems a bit large to me - am i right in that assumption?

im going to replace the PNP transistors under the drivers (level shifters? what are they there for??) and see if that helps -



Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: peavey roadmaster super duper festival
« Reply #9 on: April 09, 2015, 03:26:45 AM »
Certainly by all means check the PNP's.  In this case it's a sort of super-LTP with two devices on each side.  The PNP emitter-followers ('coz that's all they are) act like buffers on the bases of the NPN LTP and allow a much higher input impedance.

There is no DC NFB around this loop so there could well be a largish offset betwteen the LTP collectors.  As long as you still have enough voltage swing to drive each of the grids to zero volts from Vbias (i.e. 55Vpk) then you should be right.  Some voltage imbalance is common with valve LTP PI's.



(ed: typo)
« Last Edit: April 09, 2015, 01:52:41 PM by Roly »
If you say theory and practice don't agree you haven't applied enough theory.

Enzo

  • Legendary
  • ******
  • Posts: 1899
  • Chip Points: 198
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #10 on: April 09, 2015, 03:42:38 AM »
Remember, the DC collector voltages are blocked from the tube grids, only the signal gets through.  What matters is that the signal amplitude on both sides is about the same.  If one side is at a higher DC than the other, it won't matter as long as the signal is not clipped.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #11 on: April 09, 2015, 01:42:52 PM »
replaced the PNPs

have about ~160V now on each driver collector

getting ~110Vp-p on the tube grids -

next step, see if these tubes are any good!

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: peavey roadmaster super duper festival
« Reply #12 on: April 09, 2015, 04:24:01 PM »
replaced the PNPs

have about ~160V now on each driver collector

getting ~110Vp-p on the tube grids -

next step, see if these tubes are any good!

Okay, that looks really good.  :dbtu:  Did you check the transistors that came out for wrong insertion/faults (It's always good to confirm your surmise just to be certain, defensive of your rep)?


Quote from: ilyaa
i live East of San Francisco

Ah, I've been reading about your drought situation and you have my heartfelt sympathy.

While homesick in London, Australian poet Dorothea Mackellar penned the rather cheesy patriotic poem "My Country", the second verse (which is the only bit most people can remember) starts...

Quote from: Dorothea Mackellar
I love a sunburnt country,
A land of sweeping plains,
Of ragged mountain ranges,
Of droughts and flooding rains.

They remember it because it's truistic (well, except the bit about the mountain ranges, "ragged" yes, however not very tall by world standards).  But the "droughts and flooding rains" really resonate because it also seems to be a land of extremes, baked hard dry and burning for years, then suddenly - underwater as far as the eye can see; "Sydney or the Bush" as we say.

{I felt the same way myself when I was working there as a tech in a cellar, only seeing the sun as a low foggy orb at lunchtime, a deep longing for a real beach, but I managed to avoid writing any twee poetry about it - I just came home.}

So even our self-absorbed "cellphone generation" are conditioned to droughts.  The last drought in the south-east lasted seven or eleven years (depending on how you define "drought") and Melbourne water storage's were down to similar single percentage digit territory so we had a very long period of water restrictions; car washing forbidden (except for food transport vehicles and commercial car washes recycling all their water), gardens limited to hand watering for half an hour in the evening twice a week (later totally forbidden except with bore or recycled grey water), everybody encourage to take a three-minute egg timer into the shower, a steady rush on dual-flush toilets and domestic "grey" (e.g. laundry) water recovery systems, and so on.

Most of Victoria was facing a similar unthinkable situation to that California is now facing - actually running right out of reticulated water.  Some country towns depended on tanker trains.

This led to some permanent changes such as the widespread switch from water-hungry European gardens to dry land gardens using drought tolerant native species, and in my region permanent restrictions on what reticulated water could be used for.

The last year we were given a target of 90 litres per person per day, but SWMBO and I have lived on tank water where an empty tank is a very rude and expensive wake up call, and managed to get our use down to 40 litres per day for the both of us.  You have to get creative and perform triage, buckets in the shower with you to recycle on the garden, the veggie patch first priority, then established plants and trees that seem to be suffering, and to hell with the lawn (it just turns into dust bowl).  Fill your swimming pool or spa?  That's a joke, right? (but the rich can buy a truckload recovered/cleaned non-drinking water at between $0.25 and $1 a litre if they really must - a similar price to petrol).

It also caused a lot of agriculture to get serious about water conservation, and the first thing to go was highly wasteful flood irrigation of fruit trees replaced with specific drip-feed systems, many millions of dollars on irrigation canals to reduce leakage and covers for evaporation (and a vast reduction in the 90% of the gigalitres being wasted).

So I have to wonder how Californians are going to respond to this fairly new situation; are people pulling together, accepting of restrictions in a dire situation, or is it more a matter of "it's my Constitutional Right to use as much water as I can pay for"?  Certainly we have selfish "water cheats" and a system of Water Inspectors who can turn up and give you a stern lecture, but very few of the bone headed actually have to be dragged into Court.  The vast majority of coffee shop and dinner party conversations tend to include a friendly competition for a low use score, and exchanging saving and reuse tips and tricks.

Not only did the tank business boom, a whole new range of tanks suitable for suburban and tight inner city house blocks appeared, slimline to fit;



...and innovative water-fences;



If everybody co-operates for the common good {aaarrgh..."socialism"} then you can get through it, but if f!!*-You-Jack-I-M-Alright dominates then you are all going to be "up *s!!t* Creek in a barbed-wire canoe without a paddle" (not that it will matter much since even that creek will be dry) as taps stop flowing altogether and you have to get by on bottled water

It's an uncomfortable truth that a city of several million people becomes effectively uninhabitable only about 24 hours after you cut the water off, so I hope you have your zombie-bunker ready if the thirsty hoards come pouring out of SF.


(Stan Cross, 1933)

If you say theory and practice don't agree you haven't applied enough theory.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: peavey roadmaster super duper festival
« Reply #13 on: April 12, 2015, 04:19:13 AM »
amps good to go!

it was just the PI - one of the 3 channels doesnt work and the reverb tank connection is bad but the client is satisfied with a reverb-less two channel amp (one of the 3 is just a bright version) so im letting it go -

thanks, guys!

(ps: the 'ghost voltage' issue was my lightbulb limiter acting funny! gotta figure that out....maybe a bad connection somewhere)

as for the drought - yeah its starting to feel more and more real - interestingly enough australia came up a few times after i read your post, mainly as a model for what we can do/what we have to look forward to. im curious to see how regulations trickle down to us 'regular' folk. the big question here is who should bear the responsibility, joe schmo or 'Big Ag,' which consumes 80% of our water, supposedly. so far doesnt seem like the state is going to crack down on agriculture - a lot of people are talking about almonds (1 gallon of water to grow 1 almond!), most of which arent even sold here.....but as far as real change, things are pretty vague at this point....

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: peavey roadmaster super duper festival
« Reply #14 on: April 12, 2015, 07:10:26 AM »
Quote from: ilyaa
the client is satisfied with a reverb-less two channel amp

Now this is where job sheets or job reports start to become important, for a couple of reasons.

Firstly they help you track gear that has a generic fault - "saaaay, that's the third time this has come in for cooked OP bottles this year" ... leads to an intermittent bias set pot you hadn't even suspected.

Another important function is protecting you from "chancers".

Had a guy turn up at the workshop door, tweenage son in tow clutching a ghetto blaster.  "He found it in the rubbish, only wants the FM radio going".  Just as well because the cassette tape deck looked rooted, worn to death.

About four months later he turns up with the item complaining that the cassette deck doesn't work and wanting it fixed for free under warrantee.  (keeping in mind that I am obviously not Megabuck Industries and am operating as a one-man-band from my home).

"Hang on, just let me check the job sheet..."

Then it starts "Don't you stand by your work?  You fixed it and now it's busted again so you obviously didn't do a very good job blahblahbaah".

I finally get the job sheet up and read him the client instruction: "ex-tip, only FM radio, not cassette repair (impossible anyway)".  He had already given me a runaround so I told him he had had $80 worth of technician time for $40 and should quit while he was ahead.  He just grumphed and stomped off, his try-on having failed, no apology.  I hate to think how his son will turn out.

This guy was a serious case and fairly well known for his antics, but a job sheet is also your safeguard against simple misunderstanding and forgetfulness.

"But I thought you changed the output valves?"
"No, it says here next time 'coz you can't afford it this time".

They are just simple text files in a folder called "JOBS20yy";
Quote
<filename: make model serial.txt>
Date: (yymmdd)(+nnn job number that day if there is a chance of confusion)
Make:
Model:
S/No:
Owner:
Address:
Phn:

Report:
(what you found, what you did)

Parts:
Time:
Total:

{boilerplate terms and conditions if required}

Rule One: You Won't Remember.  Three months down the track the owner will bowl up and say "You remember that X you fixed for me?", and nine time out of ten I can honestly reply "No, did I?".  Unless a repair has something outstanding or significant about it, you simply won't remember yet another "replace OP tubes and rebias", or some other trivial repair.  This is where a good job sheet can help both you and the client.

Had a rack mount stereo PA amp come in with a blown fuse on one side, no other fault found.  Some months later it comes back with the same fault, except on checking with the job sheet it's now on the other channel, and again no other fault.  Huh?  What's going on here then?

"Bring me all your PA speaker leads".  Sure enough one had twisted inside the connector and was occasionally shorting, the first time it had been on the A-channel, the second on the B-channel.  It's easy to see how this could have turned into a reputation-damaging saga of recurrent returns without the actual fault being found, and how the job sheet nailed the suspicion that the second failure was on the other side, which made me look elsewhere.

Rule Two: You Never Record What You Later Need, or Murphy's Law of job records.  I scribble notes, voltages, etc., on scraps of paper at the bench (with the date and job ID) and use and transcribe these later into the actual job sheet, e.g. "B+=286V, Pout 47W".  Since these are basically letters to yourself later you need to think what you will want to know when coming back to it down time somewhere.

My dislike for drudge paperwork reordering parts comes second only to my dislike of accounting, but some is required, so using my head to save my posterior I composed order forms in a spreadsheet for my suppliers that looked like theirs and were self-calculating.  Just print that out and post it (or these days just post the order to their site).

A free and very functional spreadsheet (etc) is Apache OpenOffice.


Quote from: ilyaa
the big question here is who should bear the responsibility, joe schmo or 'Big Ag,' which consumes 80% of our water

Reading the MSM, blogs, &c, (i.e. through a glass darkly) it seems that California has yet to deal with questions that were resolved here decades ago.  People don't like to change proven methods and farmers and industry will fight back against restrictions, being asked to do more with less.

It took years to convince fruit farmers along the Murray that flood irrigation was unsustainable, and that investment in drip-feed systems was essential, but eventually they did.  My current fear is that it's eleven-thirty for California and you don't have "eventually".

Then I see how some Americans seem to knee-jerk react to being told what to do by government - even when it is obviously the right thing to do.  "Mah Freedomz!"

One long hard lesson over my lifetime has been timely reaction to an emerging drought.  When I was a teenager people just went on watering their thirsty European gardens and praying for rain, and restrictions were introduced too late to help much unless they were draconian.

We now have three Stages of water restriction and some places, such as where I live West of Melbourne, have permanent Stage-1 restrictions, no unattended lawn sprinklers for example, only hand garden watering allowed.



Well man this is what I'd call running on empty, a "Stage-4 - evacuate now" situation.  Well past putting a brick or two in your toilet cistern.

As I see it you have two forces, individualistic/anti-regulation/sectional self-interest; and you have a community that want to survive, and you will only survive if communitarianism trumps individualism.  The thing is with water, when it runs out we all run out.

This is the Climate Change problem in microcosm, we can all take a small regulatory hit now, or we can go for broke now and take a draconian regulatory hit down the track.

I have a small tank, came with the place, and between droughts it means I don't have to pay for garden water, and in drought times it keep my fruit trees going (and forget the rest).  So get a tank, even having 1000L makes a difference.

And you can get creative;



If you say theory and practice don't agree you haven't applied enough theory.