diyAudio (
-   Tubelab (
-   -   "Hazen" Mod on Simple SE? (

Davec113 31st December 2009 09:39 PM

"Hazen" Mod on Simple SE?
Looks possible on the Simple SE, you'd need to cut a trace on the board, then solder a cap between G3 and Cathode on the power tube sockets.

Anyone try it?

Tubelab_com 3rd January 2010 03:53 AM

I haven't tried it, but I would proceed with caution. This mod leaves G3 with no DC connection whatsoever. Ordinarilly G3 should not draw any current, and stray electrons that strike G3 (inevitable) will eventually build up a negative charge. However if the tube is even slightly gassy (common with current production tubes) you could wind up with a positive voltage on G3 leading to more distortion and a possible runaway condition.

If you do this, I would leave a meter connected across the cathode resistor for a while and watch for unusual current changes. G3 doesn't have too much effect on tube current, but I still like to have it connected to something (DC wise).

There was a post about a year ago by a long time tube amp designer that claimed connecting G3 to a low (about 10 volts) negative bias made G3 "dissapear". This was only supposed to work on EL34's. I never got around to trying it. The cap could be doing exactly the same thing.

Davec113 5th January 2010 07:40 PM

It's tempting to try it, but I'm not sure I want to risk damaging the amp. I guess I need to build a 2nd amp with cheaper parts to experiment on. :D

Tubelab_com 6th January 2010 01:53 AM


It's tempting to try it, but I'm not sure I want to risk damaging the amp. I guess I need to build a 2nd amp with cheaper parts to experiment on.
I don't mind blowing stuff up. In fact I have a Simple SE board that I have blown up and fixed countless times. There are pictures of different itterations of blown parts scattered throughout the "Tubes" forum. In fact the necessary runners on the PC board are already cut (for another experiment). Once I get caught up on the Simple P-P manual, I may try it just to see what happens. I imagine the results will depend on the output tubes. I have plenty of less than perfect examples to try.

Davec113 28th August 2010 06:59 PM


Since my post I've finished my ME degree and moved, nothing new happening with my system, which I'm pretty much satisfied with... as long as it stays in a small room "nearfield" it is hard to beat.

Now I am wondering if anyone tried this mod to the Simple SE yet? I will do it first if I have to...

Edit... this only works on el34s because there is no internal connection to G3, so this shouldn't have any affect when running kt88s I'm guessing as the internal connection will be present, and the cap in parallel probably won't do anything, but correct me if I'm wrong please.

rock4016 15th February 2011 06:44 PM

You are correct, you need a 6CA7 or EL34 to do the mod.

Davec113 30th May 2012 06:45 PM

Bringing this thread back from the dead, I am about to do this modification.

I have had my Simple SE for 4-5 years now, and am doing this because I need to remove the PCB to replace a failed electrolytic cap, one of the power tube's cathode bypass caps. The cap was buldged out and just started to leak, this made the cathode resistor run hot and it blackened the PCB a bit. The resistors on both sides look like they have been getting VERY hot, and they are 5W Kiwames. I am going to go with 12W Mills wirewound and place them off the pcb and away from any capacitors. I am doing the same for the 10k 5W resistors feeding the CCS, they are too close to my Mundorf SIO coupling caps. I am replacing all of the electrolytics while I am at it, and replacing the final PS cap with a Mundorf M-Tube Cap at 100 uF, which won't fit in the PCB, but I have a clamp mount for it and I can get it very close to the PCB. I also have 2 large motor run caps and a custom choke in the PS, so replacing this last electrolytic with a big film cap should be a nice upgrade. The 47 uF cap after the rectifier tube is getting replaced by a JJ electrolytic.

So for the Hazen mod, I am going to cut the traces on the PCB and solder Mundorf M-Cap ZN .1uF film/foil caps between pins 1 and 8 of the tube socket.

I will report back on my findings, but it may be a while (weeks, not years) as I am also constructing an Aikido preamp at the same time to feed the SSE, which is using a lower gain 12BH7 driver tube. My Anthem Pre1 preamp recently melted it's PT...

Davec113 18th June 2012 04:49 PM

I got all the parts in, and am in the process of replacing them.

I cut the trace between pins 1 and 8 on the PCB, luckily this was fairly easy. I replaced the trace with a wire jumper for now, as I want to get the amp back to working condition and listen to it for a while before doing the mod.

I am also eliminating the CFB and Triode/UL switches as I don't use those options and this will clean up the wiring a bit.

Davec113 19th June 2012 04:27 AM

I got my SSE up and running, source is foobar 2000 using its volume control while I get my Aikido preamp built.

The changes I made to the amp resulted in an improvement in sound quality, most noticeably bass impact and response, and increased dynamics in general. The improvements are across the board with the speakers disappearing to a greater degree, an increase in detail and more sharply defined highs. It's likely the bass and dynamics are due to the new PS caps, replacing the electrolytic in C2 with the Mundorf M-tube film cap is a pretty big (and expensive) upgrade. It's also likely the Mills resistors in the power tube's cathodes are going to sound different than the carbon film Kiwames, possibly affecting the detail and treble to some extent. Eliminating the extra wiring and switches for UL and CFB probably made a difference too.

As the amp plays it is settling in and some extra treble energy and harshness are mellowing out, I will use it like this for a while to get a handle on how it sounds, then I will replace the jumpers between pins 1 and 8 with the .1 uF film caps and update this thread.

Davec113 28th June 2012 07:44 PM

OK, so it's done. I used Mundorf ZN tin foil film caps, .1 uF, 630V, ~$8/each. They are soldered between pins 1 and 8 on the back side of the tube socket.

I think this has made a slight difference for the better, the basic sound of the amp is unchanged but there is an increase in clarity and a more "effortless" presentation. The bass notes are better defined tonally and dynamically.

The amp has been running for a couple hours and so far, no problems.

This is a pretty easy mod to try out, especially if you're building from a new PCB. This mod combined with bypassing the cathode cap with a small value film cap has made a substantial improvement in the sound quality of the SSE to my ears. Replacing C2 with a 100 uF Mundorf film cap was another improvement, although more costly.

All times are GMT. The time now is 10:12 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 18.75%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio