Mods to increase power of 300B amp

I'm thinking of increasing the amplification power of my Audio Space AS-300B MKII from 8 watts to 15 watts like Cary Audio SEI SE (which using KR 300BXLS at 15 watts). Fyi, I also intend to use KR 300BXLS for my AS300B MKII provided it will be safe for use. Any advice guys before I sent in for mods later ?

To increase the output power of the amp to 15W would require increasing the operating voltage of the 300b from around 350VDC to 700VDC. Changing the 300b tubes alone without internal modifications (quite substantial) would not increase the output power.

This would require modifying the power supply of the amp (power transformer, resistors, capacitors, etc) and output transformer to cater to higher output power. The power supply capacitors would need to have a rating of around 1000VDC, otherwise it would risk failure. All the operating voltages would need to be recomputed and resistors values may be different and require change.

Personally, I would buy a 845 or to move to a higher sensitivity speaker.

Hasnul, it will be better to improve the driver stage of the 300B. That will make more significant changes to the transients and clarity of sound. Adding a constant current source to replace the load resistor of the driver tube makes a lot of difference. I've done that and it works very well.

cheers.

Look at the power supply first if it can support the increase in output power......It will likely to create more problem if it can't....Like increase in distortion and at worst, frying the power transformer.

There is NO avenue to increase the HT from stock tranny. Its 280VAC/200mA single winding to a solidstate bridge rectifier. B+ is 365VDC.

Well, personally ive listen to a few 845 & its just isnt my cuppa tea. My vintage speakers runs fine just that im having some wild thinking. It seems it will require a lot of costly mods to get it done. Crap !! I just might have to settle for normal KR Audio 300B this way.

Tube rolling is one of the upgrade options.

You can consider higher-end component replacement without changing the basic design of the amp - upgrading coupling caps, resistors, PSU capacitors or output transformer would also bring sonic changes to your taste.

When the upgrade bug bites - it gets expensive!

hehe..ur right about the upgrade bugs !! Done some mods like Mcaps Silver/Oil on the couplings & Nichicon NX on psu side.

Perhaps i should increase the bias !! Since it was fixed biasing (I think), how to do it ?

Output trannys would be nice too but im worried about the mounting on the chassis.

300b tube Single ended bias is 60mA but thats the max for safe operation. Manufacturer will tend to bias it lower for safe level. They're not going to bias tubes to max and have you shorten the life of tubes. Use your own discretion.
Bias adjustment proceedure documented on the official website.
Gd luck!

Hasnul,

Agreed with MThoi, to increase output power u need to increase the plate voltage and in orader to do this u may need to change your power trans as well if your power trans only give u 280-0-280.

what speaker r u using now?
Does your speaker clip when at high volume?
Are you using any pre amp?

The manual on the web are revised MKII's unlike the one sold by A&L years ago. The ones locally (also MKII) are without any bias pot adj on the chassis unfortunately. So, I need to open it up to see if there any bias adj pots inside.

Im pairing with B&W DM4, a 3 way vintage circa '73-'80. No problem with loudness since power handling is 10-30 watts only based on manual. Even volume at 9 oclock it went very loud !

hasnul wrote:Even volume at 9 oclock it went very loud !

So what's your problem ??? !!!

well there aren't any problems. it's just that the price for a pair of 300BXLS are the same as normal 300B version by KR Audio. Being the advantage that the 300BXLS can be driven higher than normal thus that wild idea came to me.

hasnul wrote:The manual on the web are revised MKII's unlike the one sold by A&L years ago. The ones locally (also MKII) are without any bias pot adj on the chassis unfortunately. So, I need to open it up to see if there any bias adj pots inside.

Im pairing with B&W DM4, a 3 way vintage circa '73-'80. No problem with loudness since power handling is 10-30 watts only based on manual. Even volume at 9 oclock it went very loud !

THe bias pots are definitely inside bro...

Hasnul, kr300 b, kr300bxls, kr300b we copy r not the same. They might not be able to replace directly with normal 300b tube amp setting. U need to reset their heater voltage.

To me the kr300b we copy r the best sounding 300b among kr300b tube. No point to take the hassle trying out the bxls. The Bxls have a hard sound. As u don't need the extra power why bother?

Being the same price that triggered my curiosity. However Im gonna drop the XLS. Now there 2 variants of KR 300B. Its the baloon & the normal WE copy. Will do more research between the two.

hasnul wrote:I'm thinking of increasing the amplification power of my Audio Space AS-300B MKII from 8 watts to 15 watts like Cary Audio SEI SE (which using KR 300BXLS at 15 watts). Fyi, I also intend to use KR 300BXLS for my AS300B MKII provided it will be safe for use. Any advice guys before I sent in for mods later ?

Hasnul,

I believe the Cary 300B SEI use the standard 300B tubes. The XLS ones are special orders. May I ask why are you looking at increasing the power? Looking to achieve better tonals or perhaps to drive difficult speakers?

best wishes.

hasnul wrote:Being the same price that triggered my curiosity. However Im gonna drop the XLS. Now there 2 variants of KR 300B. Its the baloon & the normal WE copy. Will do more research between the two.

Hi Hasnul,

What type of sound do you like? The KR audio is rather Digital to my ears and you may not like them. I can also recommend you some combination of 6SN7 and 300B tubes that I have tried over the years.

Best wishes.

Ive only heard the special ordered Cary Audio SEI 300 with KR300BXLS paired with Sterling LS3/5a at Music By Design years ago. Its very analog sounding although the PRAT is very slow. Soft bass even.

But its that analog sound & tone that hooked me. I think it might be better if paired with my vintage speakers since mine is a direct rival to Spendor BC1. But I wont go for 300BXLS. So brabusm, about your recommendations ?

hasnul wrote:Ive only heard the special ordered Cary Audio SEI 300 with KR300BXLS paired with Sterling LS3/5a at Music By Design years ago. Its very analog sounding although the PRAT is very slow. Soft bass even.

But its that analog sound & tone that hooked me. I think it might be better if paired with my vintage speakers since mine is a direct rival to Spendor BC1. But I wont go for 300BXLS. So brabusm, about your recommendations ?

What type of sound do you like? Mellow, lush, thick and sweet? How do you like you bass? Will see if I can dig through my journey for you.

Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

Hasnul, I do suggest u give kr300b we copy a try. This tube is funny, it needs 1 hour to warm up. After an hour, ur amp will suddenly sounded much better. If u want more refine in the highs, then u may go for Shugaung treasure 300b the premium grade.

hasnul wrote:Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

...otherwise Rod Stewart will sound like Zee Avi ... right ?

noodle88 wrote:Hasnul, I do suggest u give kr300b we copy a try. This tube is funny, it needs 1 hour to warm up. After an hour, ur amp will suddenly sounded much better. If u want more refine in the highs, then u may go for Shugaung treasure 300b the premium grade.

Yeah, I also prefer the KR Audio 300B WE copy since the Black Treasure price aren't too far from KR's especially if buy from US.

I also heard those globe TJ meshplates on Cayin SET integrated with Audionote AZ4. Overpowering upper mids & the treble energy are too much ! Though it came with stellar dynamics & prat. Funny that most reviews on the TJ's said that it was lush sounding but I found out it was too bright !! Perhaps it was the Cayin's character ? Hmm...

mugenfoo wrote:

hasnul wrote:Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

...otherwise Rod Stewart will sound like Zee Avi ... right ?

Hahaha ! That would have been very scary !! My Sansui AU-101 & AU-70 will handle those Beetles, Deep Purple, America, Neil Young, etc. No worry's on those category.

Hasnul, I also have TJ 300b mesh plates. When play in my 300b amp, I'll rate them shuguang> kr300b we> TJ mesh.
U wouldn't be wrong if u op for kr tube.

I'll take note on that. Will have find extra funds for the tubes.

hasnul wrote:Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

Hi Hasnul,

Try this combo:

1) Use a pair of NOS Black TOP Black base RCA 6SL7GT or NOS TUNGSOL 6SL7GT
2) Gre-pin CV181 x 2
3) Western Electric 300B

Guarantee sound kao kao. You will be able to hear the twangs of the strings alongside the plucking, the glorious extensions from the pipe organ, the deep lows from the cellos as well as the natural piano notes. I was amazed at the definition I got from the combo as you can literally hear/feel the hammer striking the chords when playing piano pieces. With the vocals, it's magical. You will be able to hear all the subtle nuances from the voice. It's not about hearing the draw of each breath but more so the micro tones that makes up each breath that is sung as words are made up of a myriad of frequencies all coming through at different layers and pace. I am hoarding some so that I can listent to the same sonic signature going forward.

Steer away from the NOS Brimar 6SN7GT as they are very bright sounding like the Telefunkens. The standard NOS RCA 6SN7 are thin sounding as are the modern production Tungsols. My friend related to me that the Shuguang Black Treasure CV181 are quite good but I have not auditioned them yet.

I have heard a full compliment of TJs on a Cary 300B SEI eg 2 x TJ 300B + 3x TJ 6SN7. It is about 50% of the combination I recommended to you above.

As for the 300Bs, the KR + Shuguangs including the Black Treasure Shuguangs won't give you the thick, lush and sweet sound that you like.

Best wishes.

hasnul wrote:Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

Hi Hasnul,

Try this combo:

1) Use a pair of NOS Black TOP Black base RCA 6SL7GT or NOS TUNGSOL 6SL7GT
2) Gre-pin CV181 x 2
3) Western Electric 300B

Guarantee sound kao kao. You will be able to hear the twangs of the strings alongside the plucking, the glorious extensions from the pipe organ, the deep lows from the cellos as well as the natural piano notes. I was amazed at the definition I got from the combo as you can literally hear/feel the hammer striking the chords when playing piano pieces. With the vocals, it's magical. You will be able to hear all the subtle nuances from the voice. It's not about hearing the draw of each breath but more so the micro tones that makes up each breath that is sung as words are made up of a myriad of frequencies all coming through at different layers and pace. I am hoarding some so that I can listent to the same sonic signature going forward.

Steer away from the NOS Brimar 6SN7GT as they are very bright sounding like the Telefunkens. The standard NOS RCA 6SN7 are thin sounding as are the modern production Tungsols. My friend related to me that the Shuguang Black Treasure CV181 are quite good but I have not auditioned them yet.

I have heard a full compliment of TJs on a Cary 300B SEI eg 2 x TJ 300B + 3x TJ 6SN7. It is about 50% of the combination I recommended to you above.

As for the 300Bs, the KR + Shuguangs including the Black Treasure Shuguangs won't give you the thick, lush and sweet sound that you like.

Best wishes.

mugenfoo wrote:

hasnul wrote:Definitely I want mellow, lush, thick & sweet. Bass i'm not complaining. If I wanna play rock or pop music, I got my Sansui's to handle them.

...otherwise Rod Stewart will sound like Zee Avi ... right ?

It's not like that Mugen.

Rod sounds great on the system as is Gun & Roses, Metallica, Stevie Ray Vaughan etc. The tubes produce a different type of sonic signature for different souls...Kindred beings.