Sessionette 75 ILP 'brick'

[Mick Bailey]

Many of the Sessionettes with the ILP HY248P encapsulated power amps have failed by now, but I've just got a Mk1 in and it's still going strong after 30 years of use.

Out of interest - how many out there are still being used regularly with their original 'brick'?

[TheUnWiseOne]

Late reply to your post - but I'm new here...

My has the HY248 - I'm hopeful it's not the reason it currently out of it's normally regular service.

I've read some people have changed them and a tech here in London offers to swap them out (although he doesn't say what for!)

[Mick Bailey]

Ironically the amp I mentioned failed a few months later.

The failure modes are;

Distortion and/or volume drop
Excess noise
Cutting out

The modules are not serviceable and have to be replaced if faulty.

[TheUnWiseOne]

Ironically the amp I mentioned failed a few months later.

The failure modes are;

Distortion and/or volume drop
Excess noise
Cutting out

The modules are not serviceable and have to be replaced if faulty.

I'm not sure if mine has failed or if its the preamp - do you know what replacements will work?

[Mick Bailey]

In another post you referred to the FX return input producing a sound. With these amps you need a pretty high level signal to get a decent output, so a guitar plugged straight in will be pretty quiet unless you run it through a boost pedal set fairly high. However, you should get some output with a guitar and if this is the case (and it's undistorted) then you can check the preamp. To do this you need to run the FX send into another amp. The output is line-level so go into the second amp's low input and keep the Sessionette volume down. If the preamp is working you should get full control functionality and good sound output.

The caps in these amps hold up well. When you do get problems, the main filter caps will produce either excess hum and the amp will continue to operate, or they short and blow fuses. You can get coupling caps that dry out and cut the signal, though. Don't change any parts without knowing they're bad - the circuit boards are intolerant of excess heat and pads easily lift, so unnecessary replacement is to be avoided.

If the power amp is faulty you only have a few options. For my personal Mk1 Sessionette I designed and built a MOSFET module based on the last design they produced, though with adjustable bias and offset controls. I had plans to make a few of these, but they worked out too labour-intensive to ever be viable. Stewart Ward was selling modules, but they became uneconomical and the last I heard was he didn't intend to supply any more, but it's worth checking with him to see if any are available.

Another route is to fit a ready-made pre-assembled power amp. There are plenty of these around, but the Sessionette runs a comparatively high voltage and very limited space, so care needs to be taken in selecting something that will work correctly.

But firstly, you need to make sure where the fault lies.

[J M Fahey]

What makes them relatively easy to substitute is that Mr Awards included all his design ideas and mojo in the very good preamp, and let the power module to "just drive the speaker" and not much else.
Only 5 pins to connect: +V , -V , Ground , IN , Spk OUT.
No tricky NFB , just fixed internal one; you feed it power, inject preamp signal on one end of the brick, drive a speaker from the other end.

That's what his own replacement module did, with only the very minor inconvenience of drilling 2 new mounting bolt holes on thye heatsink/backpanel.
If you ask me, a stroke of genius

I'm quite certain that *any* 100W power module which is happy with that rail voltage and with output transistors bolted to an L shaped aluminum heat spreader which fits in the available space will work fine.

If you find any candidate at some established supplier (if possible avoid EBay) and have any doubts, post link here so we see it.

[TheUnWiseOne]

What makes them relatively easy to substitute is that Mr Awards included all his design ideas and mojo in the very good preamp, and let the power module to "just drive the speaker" and not much else.
Only 5 pins to connect: +V , -V , Ground , IN , Spk OUT.
No tricky NFB , just fixed internal one; you feed it power, inject preamp signal on one end of the brick, drive a speaker from the other end.

That's what his own replacement module did, with only the very minor inconvenience of drilling 2 new mounting bolt holes on thye heatsink/backpanel.
If you ask me, a stroke of genius

I'm quite certain that *any* 100W power module which is happy with that rail voltage and with output transistors bolted to an L shaped aluminum heat spreader which fits in the available space will work fine.

If you find any candidate at some established supplier (if possible avoid EBay) and have any doubts, post link here so we see it.

Thank you so much for your help

would something like this one be an 'ok' replacement? LA100B power amplifier module 4 to 8 ohms 45V -

[TheUnWiseOne]

Thank you for your help! I think it is something on the preamp that has failed, I get no control from the EQ- I think c19 is the cap that may have dried out (hope it's that simple!)- I've dropped in for a 20 quid diagnostic to get someone to identify the issue, I may take it on if it's relatively east for a noob (I'm handy with a soldering iron but I'm very much still leaning!) or pay to it get it fixed (I miss my tone!)

[Mick Bailey]

Here's one of my own power amp modules;

[TheUnWiseOne]

Here's one of my own power amp modules;

[ATTACH=CONFIG]39181[/ATTACH]

Thanks for this

I've heard back for the 'repair' shop chap he tells me the power amp is working - but the some thing on the pre amp has failed - but he cannot tell me what it is.

[J M Fahey]

1)m you can't mount the LA100B , it's already heatsinked !!!!
You'd need something like the "brick" part only enclosed in a U shaped aluminum channel and nothing else

2) Mick Bailey's is perfect.
My generic power module is very similar, and many others, because it's a general purpose üniversal" solution module, maybe you can buy one from Mick or get something in that line.
I'm 6000 miles away or I'd offer one of mine at cost ... but freight is a deal killer.

3) not a very good repair shop, considering the schematic is available and he could at least have traced signal along it.

Even without full repairing it, he might at least have found that "signal stops at the tone controls" or whatever.

That said, Sessionette 75 has a switch, usually called "EQ In" , which switches EQ OFF.
Maybe you set it off or old contacts got stuck or dirty and locked it in the OFF position.

Inject some MP3 at the amp input to have both hands free and check all pots and switches, in all positions, then confirm here which do NOT work.

[TheUnWiseOne]

1)m you can't mount the LA100B , it's already heatsinked !!!!
You'd need something like the "brick" part only enclosed in a U shaped aluminum channel and nothing else

2) Mick Bailey's is perfect.
My generic power module is very similar, and many others, because it's a general purpose üniversal" solution module, maybe you can buy one from Mick or get something in that line.
I'm 6000 miles away or I'd offer one of mine at cost ... but freight is a deal killer.

3) not a very good repair shop, considering the schematic is available and he could at least have traced signal along it.

Even without full repairing it, he might at least have found that "signal stops at the tone controls" or whatever.

That said, Sessionette 75 has a switch, usually called "EQ In" , which switches EQ OFF.
Maybe you set it off or old contacts got stuck or dirty and locked it in the OFF position.

Inject some MP3 at the amp input to have both hands free and check all pots and switches, in all positions, then confirm here which do NOT work.

Thank you again! A novice like me really appreciates the advice!

Very annoyed with 'repair' shop - filled me with hope he could tell me the problem!

6000 miles might be difficult...

[TheUnWiseOne]

Thank you again! A novice like me really appreciates the advice!

Very annoyed with 'repair' shop - filled me with hope he could tell me the problem!

6000 miles might be difficult...

As an update -

I swapped out the TL071 and first tl072 because my dad had a couple - playing an mp3 440 into the input I can use the channel B vol and tone pots and they do adjust the tone - the guitar doesn;t seem to give any though...

[Mick Bailey]

Some repair shop. Maybe a good living can be had from charging £20 a pop to tell a customer you can't fix something. Not much job satisfaction, though.

Did you try connecting the FX send to another amp?

[TheUnWiseOne]

Some repair shop. Maybe a good living can be had from charging £20 a pop to tell a customer you can't fix something. Not much job satisfaction, though.

Did you try connecting the FX send to another amp?

I refused to pay! It was the hope he generated that miffed me more! He went from confident he could tell me one day to sheepish the next!

I've tried connecting FX send into another amp and I get a crackled distorted tone if I strum hard (ooerr missus)

If I play a 440 test tone from my phone and youtube its much clearer through internal speaker.