Kits useable with a M500 300B Monoblock amp - Page 2 - diyAudio
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Old 5th October 2010, 10:28 PM   #11
tinitus is offline tinitus  Europe
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Im not sure, but could be the small polarised cap across the red resistor

are you sure you want to mess with that
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Old 5th October 2010, 10:38 PM   #12
Jogi is offline Jogi  Germany
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Hi Bruce,

its not Thorsten, but as I have heavily modified Ladydays, I feel somehow responsible...

The cathode cap should be the small one right under the .47 Mundorf, which is soldered across the small red resistor. Possibly someone changed it already to a better one, together with the mundorf.
In case you don't have a film cap with that big size, you could try a 100 or 47F Oscon Sepc or if not available a Oscon SA, which is an older version. Film caps are better, as Thorsten pointed out, but these Oscons are close.
It should also be rewarding to change that resistor for a very good one with the same value, a Takman 0,5 watt is a good choice, where the metal film is a bit more on the clear side, the carbon film on the warm.
But the heater supply is clearly most critical, and the CCS is a nice upgrade too.

But, honestly, the biggest upgrade is surely changing the driver valve to something more suitable for the 300B. I tried 6sl7 both systems paralleled, then with CCS, but ended up with C3o in pentode mode, a 6.3 Volt Version of the C3m. And this is how it will remain for sure, its miles ahead of all the other drivers I tried.
Also very good was the E81L as pentode, which also has a 6,3 Volt heater and could be used with your power transformer, but with a different tube socket.
I tried quite some drivers during the last years, its fun and you can learn a lot.

cheers,

Jogi
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Old 6th October 2010, 03:21 AM   #13
bprager is offline bprager  United States
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Unfortunately, I don't know the history of the amp so don't know if what is there is standard from Opera or was changed.

That the small cap is the one in quesion makes sense. The printing on the cap was cut off right where the outer wrapper goes to the edge, so the value was half cut off. So I could read a 1 and that was about it making me unsure I had the right one.

I may play around with driver tubes, but thought I would start with these mods first, see how it sounds and if OK, call it a day.

Basically I'm just trying to optimize what I have as much as practical as I listen to it for many hours a day (housebound) and even unmodded, its pretty decent making me think that some basic mods should do it.

I appreciate all your help and suggestions. Its all great and I'm learning a lot.

Bruce
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Old 6th October 2010, 06:27 AM   #14
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by bprager View Post
That the small cap is the one in quesion makes sense.
I have Brian's okay to post up the schematic of the old Billy Kit. I will do this later or tomorrow (sorry, pushed for time) and I will also try to mark on your Photo's which part is which.

From your Photo's the Amp's look completely stock, I wprked on quite a few, they all pretty much look like this.

Ciao T
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Old 6th October 2010, 02:41 PM   #15
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by ThorstenL View Post
I have Brian's okay to post up the schematic of the old Billy Kit. I will do this later or tomorrow (sorry, pushed for time) and I will also try to mark on your Photo's which part is which.
Okay, here part 1 - the schematic for the M500 Kit sold by diyhifisupply a long time ago, which is 99% identical to the assembled M500 from Opera. The marked up photos tomorrow.

Ciao T
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Old 6th October 2010, 03:39 PM   #16
bprager is offline bprager  United States
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One difference, though not large, is that the high voltage tap on mine is 415V, not 450V.
All the other voltages are identical.
I rechecked the high voltage to be sure and it was 415, so I guess they fiddled a bit with that voltage. I remember you saying that it was on the high side, so maybe they lowered it a bit.
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Old 6th October 2010, 04:51 PM   #17
bprager is offline bprager  United States
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Since I needed a 47R and one of the other mods has me move the locations of some resistors, I decided to fill out the order with replacements for the chinese resistors in the tube section (its only a couple on each amp).
I picked the premium japanese carbons in the 1W range. Does that seem appropriate?
They didn't look like 2 watt resistors and the only other choice was the Tantalums, unless you feel the Tantalums would be a better choice.
I chose the Prem. Carbons based on some of the suggestions that have been made, what was on a few of your links and of course, the information on the DIY site.
If you feel the Tantalums would be more appropriate, please let me know, I'm sure at this point that another couple resistors won't break the bank.:-)
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Old 6th October 2010, 05:05 PM   #18
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by bprager View Post
Since I needed a 47R and one of the other mods has me move the locations of some resistors, I decided to fill out the order with replacements for the chinese resistors in the tube section (its only a couple on each amp).
I suggest you belay the order a little more. Let's be clear which modifications you are comfortable with and which not etc...

Ciao T
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Old 7th October 2010, 12:23 AM   #19
bprager is offline bprager  United States
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I actually don't have a problem with any of the mods, I have built Scott amps from the chassis up.
My questions here are because I am not an amp designer so I don't have a clue as to what mods might be best while your knowledge is far, far larger.
However, once I know what mods are needed, making the mods, whether electronic or physical is quite comfortable, I have a full machine shop and electronics shop and a wife who can use the equipment I can no longer use.
If I could have your knowledge and experience, I could probably spend all my days quite happily designing and tweaking electronics, but I'll more than settle for the incredible kindness you have shown in sharing your knowledge so that I can get these amps to really sing.
That also applies to all of you who have so kindly shared your knowledge and experience. It is greatly appreciated by someone to whom music has become far more than just a hobby. Thanks to all, and especially to Thorsten!!
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Old 7th October 2010, 12:29 AM   #20
bprager is offline bprager  United States
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One thing I do need to ask, I have studied the WE91 mod schematic and gone to the link you provided. I have read that info and downloaded the other appropriate mods.

However, the basic mod appears to be the introduction of a 10uf cap in front of the choke, with the movement of the 220uf caps to after. While this is clear, I have read comments about the "full" We91 mod.

Is the change above the full mod, or do I need to add and/or move additional components in order to accomplish the full mod?

Thanks, Bruce P
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