Icon 25 MKII Boutique HiFi tube amp

[Mars Amp Repair]

Hello folks,
I've been out of the field for a bit but will be starting up a part time garage business where my wife & I now live outside of Boise, ID repairing the usual musician's equipment but also adding vintage hifi stuff to that. Like many I repaired all that stuff a million years ago and now there is a resurgence in interest.

The question today is I am working on a boutique stereo tube hifi amp by Icon. It's British made. Uses a couple of 6SL7's as preamp & a 6SN7 as split inverter to drive the EL34 power tubes.
It's a super linear low distortion design using hand wound output transformers that have the grid taps also for ultra-linear operation. You can turn the volume full up and hear almost no hiss at all. I suppose it would probably really stink as a guitar amp (;- ).

Anyway, all that is wrong with this amp is the ac input inrush current limiter burned up. as a result, I can't read the numbers on it. I have inquired with the company to see if they'll give me some information on the device but have a suspicion that you guys with some experience with these will be able to tell...'Oh, just use a 10ohm 250V inrush limiter & it will be fine...or something of that nature.
Any ideas?
Thanx, Glen...formerly of Mars Amp Repair

[The Dude]

A) There are all sorts of web pages with articles on calculating values for inrush thermistors. You'd have to make some measurements if you wanted something proper.

B) A lot of Fender amps use the C60-11. Might be close enough.

Plan C. IMO, solder in a jumper and install a slow blow fuse. There are plenty of amps out there without inrush thermistors.

[Enzo]

OK, Just use a 10 ohm and it will be fine.


Think about it. All it is is a low resistance series part, that after a moment to warm up drops to even lower resistance so as to disappear. SO it doesn't matter if it starts at 10 ohms or 15, so long as it goes to near zero once warm. Who cares if the amp takes 4 seconds or 7 seconds to warm up?

You have any of the inrush limiters still in stock from common amps like Fender or Bugera? try one of those.

You maybe can't READ it, but you can measure the diameter. That is usually part of the part number

[Mars Amp Repair]

My first inclination was to just jump the thing, but with these hi-fi audiophile quirky types ya don't want the tech that follows you making a big stink about something that ultimately doesn't matter (probably would if he were that type anyway). I'm pretty sure I have an inrush device that will work fine.
Also about this amp, it is hand wired of course, but there are no turret strips in it. The electrolytic caps are actually glued onto the chassis by their tops & become the turret strips for other components. There are resistor networks that are just floating between tube sockets & other components. It's super clean & all leads are bent at 90deg, but how much fun is that glued-in cap going to be to replace esp if you don't have close dimensions. Also, there were high voltage leads just milimeters from ground busses. Not really a good design at all. Why no turret strips? They're cheap. IMO, that's just dumb. see attached. Thanx Enzo & 'The Dude'. glen

[Jazz P Bass]

That amp looks like it was a nightmare to assemble.

[Mars Amp Repair]

Right! Why they wouldn't use terminal strips to make that easier to have less skilled techs assemble it is beyond me. It retails for nearly $2000.00 depending on the tube compliment you request. It has no tone section and these folks just run their entire system at Flat...I haven't looked but I suppose this company probably offers a tube eq...probably for $900 or something...Makes for an easy charge on the repairs, tho as opposed to a $300.00 Line 6 where just replacing power tubes and a repair approach what they paid for the thing!...I still prefer guitar/bass amps...glen

[Justin Thomas]

They're even worse to repair...

I love true PTP & use it myself, but having to get through literal layers of good parts to reach a bad one is just... Bluh.

Justin

[Leo_Gnardo]

The electrolytic caps are actually glued onto the chassis by their tops & become the turret strips for other components. There are resistor networks that are just floating between tube sockets & other components. It's super clean & all leads are bent at 90deg, but how much fun is that glued-in cap going to be to replace esp if you don't have close dimensions. Also, there were high voltage leads just milimeters from ground busses. Not really a good design at all.

"British electrician style" as one of my former employers would say. He's English, he would know... Just slung together, bottom line - it works and can be sold. Safety requirements, who needs that? No worries as long as the "authorities" don't have a look inside.

[Jazz P Bass]

Welcome back Glen!

[Mars Amp Repair]

Thanx Jazz...nice to be back...

[pdf64]

Icon would not supply me with a schematic when I had an ST60 in for a checkup a few years ago ('send it to our service centre').
I sketched it out and was surprised it was really basic, no different to a guitar type power amp apart from UL, no fancy Macintosh style touches.
It sounded fine and put out the rated power.
The OTs were massive, obviously very high spec.
Yes the use of use of closely adjacent buss bars for 0V, HT etc seemed 'less than ideal' from a build / service perspective, but in reality I can't envisage how they might cause a problem for the user.

[Mars Amp Repair]

Well, thanx for that perspective. I wasn't actually referring to those two buses being too close together but a few components leads that were just dressed to closely by whomever built this particular amp.
Yes, either way as long as it sounds good the end user wouldn't be the wiser. BTW, Icon hasn't replied as of yet. We'll see. As i mentioned i just used a inrush thermistor from as SMPS from a tv that fit the basic parameters. It worked fine.
I was surprised when the customer balked a bit at what i considered to be a very reasonable charge esp on a $1500.00 boutique amp. Here in The Treasure Valley there are very few servicers left and only a couple that even work out off their homes.
This guy was going to ship it to Portland before he found the shop in working for now. You know what that would have cost just in shipping. Oh well.
Thanx, Glen

[The Dude]

It figures a guy who can afford a $1,500 amp would whine about a reasonable repair charge. I've often found that people with the most money have the most difficulty parting with it.

[Mars Amp Repair]

Of course the obvious reply is 'That's why they have so much money'! 😁