Found Pair Hafler XL-280 with PA-1 Musical Concepts boards

[_Mod_Man]

Hello, I’m brand new on this forum. Haven’t worked in elecs in decades... last job was a hybrid MusicMan guitar amp repair...
Anyway, I just bought this pair, with a ton of related gear, from a retired party/event singer (all for $200!!!).
These each have a MC sticker with serial number pasted neatly on their bottom, stating “PA-1/Rewire”—I’m assuming these were done AT Musical Concepts, and not sold as a kit for the end user—or does/did MC supply such stickers with their kits? (I haven’t called them yet, sorry, should I?) These amps each have a central RCA input on their rear panel, flanked with a single + and - speaker binding post on each side. So I assume these were meant to be a monobloc pair. . . Each has 4 (78000 üfd?) electrolyte caps, which are black Mepco/Centralab make.

Before I even power up, I am wandering if these are the original Caps or not, and if I should bring them up slow on a variac. I don’t know how long since these were powered up, forgot to ask, but I suspect a decade. I see that MC sells a new cap upgrade kit, should I just go ahead and do that? ***Beofre posting this I opened the second unit, and notice both power supply boards have smaller yellow caps marked Musocal Concepts, so
I guess MC also upgraded the power supply! (-;

Also, although the serial #s on the MC stickers are somewhat far apart, the 4 PA-1 boards are the same. Each has two EMPTY FUSE HOLDERs; each amp has a Single ceramic fuse in the right line in. I’m
Assuming they are jumpered or not needed..? Haven’t looked under board yet.

Also, is the single large transformer, with a copper shield over part of core, original? I’d love to see a pic of an original XL-280 chassis, if out there, to see what was original.

My intention was to use these in a home listening room, to replace my stolen Macintosh MC-75s (yeah, this ‘bargain’ doesn’t really make that sting less, I’m a tube person. . . Trades maybe?) Should I use these as is (assuming they are working, or after I repair them)? What are the PA-1 board specs? Sound quality? Does anyone out there have a pair, or has anyone heard a pair of these with this mod? Thanks in advance.

 

[Blue Shadow]

bunch of images on the web, just google it. Those are going to be some nice amps.

The main musical concepts proponent here passed away a couple years ago but dshoaf did say that they are world class. But they are sand amps and not tube so whether you like them or not is the thing. MC might be able to tell you what you have as they have a long list of upgrades for the amps.

 

[mondialfan]

The 7800 uF Mepco's are original so if you are concerned about them and have a way to bring them up slowly then you should do so.

The Musical Concepts capacitor offerings are going to be very pricey. I'd look into sourcing replacement caps from Mouser or Digikey. Go with an 80V rated with a similar size and screw spacing. The power supply boards on top of the 4 main caps are single sided and very basic and you could easily slot the capacitor mounting holes a bit with a small round file to allow for a slightly different screw spacing.

As far as the rest of your questions, The PA-1 boards are quite old, MC is up to PA-7 now. I'd just try them and see how you like them. If they don't measure up then you should be able to make money on them if you decide to resell them in tested and fully working order.

 

[_Mod_Man]

The 7800 uF Mepco's are original so if you are concerned about them and have a way to bring them up slowly then you should do so.

The Musical Concepts capacitor offerings are going to be very pricey. I'd look into sourcing replacement caps from Mouser or Digikey. Go with an 80V rated with a similar size and screw spacing. The power supply boards on top of the 4 main caps are single sided and very basic and you could easily slot the capacitor mounting holes a bit with a small round file to allow for a slightly different screw spacing.

As far as the rest of your questions, The PA-1 boards are quite old, MC is up to PA-7 now. I'd just try them and see how you like them. If they don't measure up then you should be able to make money on them if you decide to resell them in tested and fully working order.

Thanks. I have no reason to believe anything is wrong with them, except their age. I just want to err on side of caution. Recently moved—WHERE did I pack my Variac??? Lol. The seller was very straightforward, but did have them advertised as ‘tube’ amps, and when I was picking them up, explained how they sound better once warmed up. (-: He was also drinking beer and was kind enough to offery one when I arrived in my car in the early afternoon. . . The power supply boards are the original Hafler-marked PC-41b, but each has four yellow Musical Concepts 2.2 mfd caps along side, which somehow at first glance kept me from seeing that the board itself IS marked Hafler.
My main question is why the 2 fuseholders in each PA-1 board are empty. Without dismantling, I can’t see enough to tell if they are needed or not. A schematic would be very useful. I wonder if this mono conversion somehow obviates their need.

 

[_Mod_Man]

The 7800 uF Mepco's are original so if you are concerned about them and have a way to bring them up slowly then you should do so.

The Musical Concepts capacitor offerings are going to be very pricey. I'd look into sourcing replacement caps from Mouser or Digikey. Go with an 80V rated with a similar size and screw spacing. The power supply boards on top of the 4 main caps are single sided and very basic and you could easily slot the capacitor mounting holes a bit with a small round file to allow for a slightly different screw spacing.

As far as the rest of your questions, The PA-1 boards are quite old, MC is up to PA-7 now. I'd just try them and see how you like them. If they don't measure up then you should be able to make money on them if you decide to resell them in tested and fully working order.

Thank you. I found a few of (Dave?)’s posts. He seems to be a lost treasure now, would have loved to have chatted with him. . . Anyway, once I find my Variac, yes, I will bring them up slowly. I found no visual or olfactory evidence of any old burn or problems. I’ll keep my toes crossed. I am a ‘tube-sound’ guy however. . .

 

[qdrone]

Call John Hillig,you can get number off Musical Concepts web page. Your in for a treat, Hafler was John's baby, there is no one out there that can modify Hafler better than him.
I have had a Adcom 555 amp, Adcom 750 pre and a magnavox 16 bit cd player modified at Musical Concepts with great results.
Hafler uses MOSFETS, and with the mod will sound very Tubey. The review in Absolute Sound on my 555 mod stated John turns the amp into a very tubey sounding amp with controlled base and an airy high end without etchyness.
Good luck.

 

[mondialfan]

You might post a few pictures of the interior of one of the amps. The two fuses on each board should be the B+/B-. Unless someone bypassed these fuse holders, which wouldn't be smart, then their being out is not a good sign.

If you need to install new fuses then I would replace them with a much lower rated fuse like a 1A rated fuse for initial power up and basic testing before installing the proper rated fuses. A dim bulb tester would also be a good thing to use. Do a search if you're unsure of what that is.

 

[_Mod_Man]

You might post a few pictures of the interior of one of the amps. The two fuses on each board should be the B+/B-. Unless someone bypassed these fuse holders, which wouldn't be smart, then their being out is not a good sign.

If you need to install new fuses then I would replace them with a much lower rated fuse like a 1A rated fuse for initial power up and basic testing before installing the proper rated fuses. A dim bulb tester would also be a good thing to use. Do a search if you're unsure of what that is.

Thanks. These are listed at each drawing 1200 watts!!! So, I think even a 100-watt bulb is too low for a dim-bulb test. And, who has incandescant bulbs anymore! (-:
Anyway, if you saw my earlier reply, I *ALWAYS* bring up old gear on my Variac, except, after moving, I still cant find it... Which why in my initial post I asked 'if I should'-meaning, can I get around it... I have a working 'scope now, so, once I find my Variac and a signal generator... But I *am* getting impatient to power these up. And I did finally speak with John Hillig last week. He said that he did sometimes supply stickers with boards. He also says to use 2-amp fuses when I power up and test.

 

[mondialfan]

A variac will not provide the safety that a DBT will. By the time you realized something is not right while bringing up a variac you've already blown a fuse, seen smoke or heard a sizzle. The damage is done... The DBT can many times prevent this. I own both and I always use the DBT feeding my variac after mods or on any gear that's questionable. I routinely bring up amps which are much more powerful than the XL280 on 72W and 100W lamps. A 100W lamp should suffice for the 280 as long as the bias isn't cranked to max. If it is then turn the bias all the way down and try again.

 

[damacman]

A variac will not provide the safety that a DBT will. By the time you realized something is not right while bringing up a variac you've already blown a fuse, seen smoke or heard a sizzle. The damage is done... The DBT can many times prevent this. I own both and I always use the DBT feeding my variac after mods or on any gear that's questionable. I routinely bring up amps which are much more powerful than the XL280 on 72W and 100W lamps. A 100W lamp should suffice for the 280 as long as the bias isn't cranked to max. If it is then turn the bias all the way down and try again.

Who uses a variac without monitoring current?

 

[mondialfan]

BTW there are a lot of DBT designs out there some very fancy. I liked the KISS type. Mine can be built for a few bucks.

 

[_Mod_Man]

Made the pilgrimage to my childhood home...
Reunited with my babies!

 

[_Mod_Man]

Call John Hillig,you can get number off Musical Concepts web page. Your in for a treat, Hafler was John's baby, there is no one out there that can modify Hafler better than him.
I have had a Adcom 555 amp, Adcom 750 pre and a magnavox 16 bit cd player modified at Musical Concepts with great results.
Hafler uses MOSFETS, and with the mod will sound very Tubey. The review in Absolute Sound on my 555 mod stated John turns the amp into a very tubey sounding amp with controlled base and an airy high end without etchyness.
Good luck.

Thank you. I just found TWO of my childhood Variacs (see pic below) and have an oscilloscope again. I'll throw together a dbt, probably with an isolation trans for good measure, but I still need a signal generator... Almost ready to jump back in and power these up... I am amazed at my patience, as the temptation is worsened by seeing them several times a day. (-;

 

[rcs16]

In my DBT, I used two switches, one for the main power and the other switch to by-pass the lamp, it just makes it more convenient, in that you do not have to remove the plug to apply direct power.
Incandescent lamps are getting scarce, but special apps like brooder/heat lamps are still available at farm supply stores.

 

[_Mod_Man]

In my DBT, I used two switches, one for the main power and the other switch to by-pass the lamp, it just makes it more convenient, in that you do not have to remove the plug to apply direct power.
Incandescent lamps are getting scarce, but special apps like brooder/heat lamps are still available at farm supply stores.

Ha! When I went to CFLs I kept the old bulbs. I recycled the CFLs when switched to LED-CFLs are TERRIBLE. But I still have those incandescent bulbs! (-;

 

[Blue Shadow]

Incandescent lamps are getting scarce, but special apps like brooder/heat lamps are still available at farm supply stores.

rough service bulbs are still available, too. Whether they have a stronger filament or are plastic coated (teflon?) both make them a bit better for a bulb that is going to be used and abused. I guess there are some that have a dbt permanently installed on the bench but many have one that is an occasional thing making the rough service bulb a good idea.

 

[_Mod_Man]

In my DBT, I used two switches, one for the main power and the other switch to by-pass the lamp, it just makes it more convenient, in that you do not have to remove the plug to apply direct power.
Incandescent lamps are getting scarce, but special apps like brooder/heat lamps are still available at farm supply stores.

That’s a smart idea!
Lol because that transformer “” was made a stone’s throw from my new farm:

 

[kjlgpw]

Maybe you've already found out about the empty fuse holders. They were speaker fuse holders which were removed when the amp was converted to a monoblock