Mini HRM/86 Special build

[bluesfendermanblues]

The 12 x 2" cost £30 +VAT for the pair.

Contact Paul here and send him a DXF file of what you need

info@furnells.com

I don't think the postage will be too much.

Thanks for the tip ! I'll contact him as soon as I have the front and back plates made. I'm just beginning to learn the Inkscape software. Very slow process

Try this its very easy - even I did right first time!

http://www.schaeffer-ag.de/de/download/ ... igner.html

Ditto, that.

I've used Schaeffer for 1176 and SSL compressor clones. And I can confirm that they provide top quality and fast delivery. Not cheap, though.

[rogb]

Thanks for the tip ! I'll contact him as soon as I have the front and back plates made. I'm just beginning to learn the Inkscape software. Very slow process

Try this its very easy - even I did right first time!

http://www.schaeffer-ag.de/de/download/ ... igner.html

Ditto, that.

I've used Schaeffer for 1176 and SSL compressor clones. And I can confirm that they provide top quality and fast delivery. Not cheap, though.

I kind of meant use the free software to output a dxf file .
Schaeffer are great but very expensive

[mat]

I kind of meant use the free software to output a dxf file

How did You get it to save as -dxf ? I see only -fpd option.

[rogb]

I kind of meant use the free software to output a dxf file

How did You get it to save as -dxf ? I see only -fpd option.

Try "export"

[mat]

I kind of meant use the free software to output a dxf file

How did You get it to save as -dxf ? I see only -fpd option.

Try "export"

Thanks I'll try that.

[rogb]

Hi guys, this is the story so far... and it's not all good

Finished the build on Wednesday, did all my checks, everything seemed fine so I hooked up the bulb limiter and fired her up. Bulb went bright then dimmed, looking good so far.

Checked the B+ at the recto and it was 207v, seemed a bit high, also heaters at 3.5v each. I followed the 100R "virtual" CT and didn't use the heater CT.

Hooked it up to the mains, and a loud hum from the PT on standby, flipped the ON and the led indicator was on and quite bright, B+ still quite high.

Put in some bench tubes I had lying around and connected the speaker, heaters on OK but with 7v quite bright, flipped the power, the hum was there still and the el84 started to redplate. I had an HV fuse on the HV CT (0.5A) and this popped. Mains fuse was 2A slo which I guess was quite high.

If I touched the tip of the input cord, there was sound coming through, but before I could check any voltages, the el84 redplated again and the mains fuse popped. The PT was now really hot and smelling bad.

I popped another mains fuse in and it blew straight away.
The PT was nearly smoking so I guess it now had a dead short.

Got in touch with Azatplayer who is corresponding with me on this build and he mentioned the 2 diode fullwave recto as per AX84, which I didn't have.

I mostly followed the Colossal schemo for the PS and that had a 4 diode bridge recto which I used. Apparently this is wrong with a Hammond 269/369 CT PT.

Anyway the PT was toast, so I got in touch with Phil at Bluebell Audio to order another. He confirmed I needed just the 2 diode full wave. And a place on Rectifier 101

Thinking this was going to be an expensive lesson, I ordered it but there are none in the UK so it is coming from Canada next week. The incredible quality of this man Phil is that he is letting me have this at cost to help me out. My mistake, but he doesn't want to profit from it.

The problem for me is I get a bit confused. I have been trying to build a hybrid from 3 schematics, the EF86 with the 101 HRM preamp and the AX84 power amp. I hope I have learned a lesson here and that no other parts are damaged - fingers crossed.

During this down time, I am going to replace the diodes with 2 x UF4007 and recheck all of my wiring and connections. Mains fuse is now 1A.
Heater CT will be tied to pin 3 cathode EL84.

To cheer myself up, I bought a new temp controlled solder station and ditched my cruddy old iron, so I hope some of the "bumps" in my build can now be a thing of the past.

Many lessons to be learned on this build, but I am not too down at the moment, it's warm and sunny here in England, which is unusual in April

All the best
Rog

[Guitarman18]

Hi Rog,

Sorry to hear about your unfortunate events with your build. I bet all of us have learnt some pretty expensive lessons in the past, but at least you were unharmed and can move on from this one.

I can also vouch for Phil at Bluebell Audio, he has sorted me out on a number of occasions. He's very knowledgeable and can talk the hind legs off a donkey!

Thanks for sharing your experiences and best of luck with the replacement parts.

Cheers,

Paul.

[Structo]

Did you use the center tap of the transformer with a bridge rectifier?

[rogb]

Did you use the center tap of the transformer with a bridge rectifier?

Hi Tom, yes - center tap to ground (fused) with a 4 diode bridge

[rogb]

Hi Rog,

Sorry to hear about your unfortunate events with your build. I bet all of us have learnt some pretty expensive lessons in the past, but at least you were unharmed and can move on from this one.

I can also vouch for Phil at Bluebell Audio, he has sorted me out on a number of occasions. He's very knowledgeable and can talk the hind legs off a donkey!

Thanks for sharing your experiences and best of luck with the replacement parts.

Cheers,

Paul.

Thanks Paul, I think you can understand the stuff I've been throughI have spent most of today redoing my speaker and effects loop jacks and I put a 66k (measured) slope into the 50 watter, had it on fairly loud but couldn't hear much more bloom. But I could get a little more marshmallow feeling in the bass lol.

[ampbldr2]

Rog,

Sorry to hear about your build problem. As others stated that you are not harmed. Wish you good luck on the rest of the build. So far your cab and chassis look really good.

A few year ago i was building a High Octain and i fired it up without a bulb limiter. The hammond 269 started smoking and i scratched my head on that only to find out one of the diodes i installed was a dud and direct short causing the pt to fail and smoke. In the end lesson learned measure all my parts before installing.

[bepone]

hello rogb, sorry for hear that. i have some concerns with your EL84 wiring. redplateing shows that something is bad there. please if you can give us one picture which shows connection of EL84 socket.

did you use pin ONE of EL84 which datasheet stated that is I.C. , as an anchor point, (usually for the G2 resistor)?

this practice is fine for most "modern" 84's but NOS valves will have pin 1 internally connected to G1, and will self destruct..

[Structo]

I just wanted to confirm with you that you can't use the HV center tap when you use a full wave bridge recitifier.

That is what smoked your transformer.

The one side of the bridge goes to ground instead.

The thing I try to remember is:

As a general rule if the transformer doesn't have a CT you have to use a fullwave bridge.
If it has a CT then you use a full wave like Fender.

Sorry you smoked your PT but I can almost guarantee you that you will never do that again.

[rogb]

hello rogb, sorry for hear that. i have some concerns with your EL84 wiring. redplateing shows that something is bad there. please if you can give us one picture which shows connection of EL84 socket.

did you use pin ONE of EL84 which datasheet stated that is I.C. , as an anchor point, (usually for the G2 resistor)?

this practice is fine for most "modern" 84's but NOS valves will have pin 1 internally connected to G1, and will self destruct..

Thanks Bepone, only pins 2.3 7.9 as per the AX84 schemos and Colossals mini HRM schemo.
The redplating was caused by my center tapped HV and the full wave bridge recto.

[rogb]

I just wanted to confirm with you that you can't use the HV center tap when you use a full wave bridge recitifier.

That is what smoked your transformer.

The one side of the bridge goes to ground instead.

The thing I try to remember is:

As a general rule if the transformer doesn't have a CT you have to use a fullwave bridge.
If it has a CT then you use a full wave like Fender.

Sorry you smoked your PT but I can almost guarantee you that you will never do that again.

Thanks Tom, a lesson learned, got some UF4007s on the way so it should be maybe a touch quieter with them anyway.

Yep the other side of the bridge went to ground, no wonder the voltages were a bit crazy, let's hope no more harm done.
Bluebell Phil is going to talk me through the PT hookup wire by wire just to be safe, now THAT'S customer service