Mr. Liang audio amplifiers

[sorenj07]

Re: Alternative circuit for Liang with 300b

Hi,
I found this and lit looks like a better use of the 300B as a driver. Any comments?
Ciao

I'd rather see that 300B as a cathode follower DC coupled to the grid of the 845...

 

[phi70]

300B is a cathode follower on the Liang when stock

and its coupled via a 0.47 and a 1.2k resistor to the grid of the 845.
The suggested design using 6SN7 probably calls for removal of the front PCB and rewiring
everything p to p.

 

[toufu]

I have a Liang 845 L1 (I think, maybe L2) and I drove it to Quad 12L2 speakers, which are rated at 88db. It sounded great in my medium sized room, this is with the dial at 12 or 1 O'clock. Now I have upgraded to Zu Druids, I only need to dial at 9 or 10.

 

[phi70]

Mine distorts at 1oclock volume when driving

avalon eidolons (yes yes I know its not the right speaker for this thing, am rounding up different speakers to match)

Happens even with just vocals.

Overall it has a pretty rough and uncivilized sound.

Will check voltages of key testpoints later to see if anything is off.

BTW mine has 6AC7+300B+845 with brass bass.

 

[toufu]

Something must be off, mine is the 845+6AC7+6L6G version. It sounds beautiful. I would think the L3 (300B) version should sound even better.

 

[phi70]

any chance you can share with me the 6AC7 voltages

on cathode and plate?

I checked the 845 voltages and they are sane.
I did not expect even a 15 Watt amplifier to start to clip that soon.

 

[Mush]

Mr. Liang 845-3 Voltages

Here's PDF of some voltages I took a while back for the 300B model.

 

[GTHICM]

Driver Circuit

I too have a Liang 845 LS5 and have been lurking and reading this post for some time. I have seen different suggestions for the driver circuit, including that proposed by Lampizator. I was wondering if anyone other than Swampy has actually implemented a different circuit. It would be interesting to hear impressions. The 6SN7 input to the 300b Mush posted looks promising.

 

[phi70]

Thanks Mush for the reference voltages

I took the leap and re-capped everything... those "LICON" caps are no damn good. In goes 8 x Nichicon 390UF 450V + a bunch of others, Hexfreds for the high voltage and 16 Schottky's for all filaments.
Gone is the hashy rough flat and uncivilized sound.
Even with the 6AC7 driver this thing sounds magical,
still won't drive Eidolons but will drive ProAc Response 3.5s to perfection.
This thing is one hot bargain at a few hundred bucks.

 

[Mush]

I screwed up. There's a typo for the 845 cathode voltage. The calculation is for the current is too high. I think the correct value for the voltage should be .855 volts which will give 100ma.

 

[Mush]

Phi70,
What are the part numbers for the diodes and caps? Where did you source them from? I want to eventually rebuild the Liang.

I am considering converting it to 813 since they are significantly cheaper than the new 845. People that have subbed the 845 with the 813 have consistently claimed that it sounds better. Oddly, the Shuguang 813 is reputed to be better than American NOS. It's only about $45 so I can afford to stock up. The only caveat is that it needs a 5A filament supply. I've found a 10vct @ 3A Triad transformer from Allied Electronics that look like it could serve if a pair is run in parallel.

 

[phi70]

Your voltages differ slightly from this variation of L845, parts used for ugrade are:

but not a big diff anyway.
The parts I used are:

Digikey:
493-2617-ND 5.24700 52.47 T
CAP 390UF 450V ELECT LS SNAP
SCHED B: 853222 ECCN: EAR99
LEAD: LEAD FREE ROHS: ROHS COMP

Mouser:
647-UPT2D101MHD
Nichicon Low Impedance Aluminum Electrolytic Capacitors - 105 Degree
100uF 200V
ECCN:EAR99 3 3 1.080 3.24
2 1
511-STPS8H100D
ST Power Schottky Rectifiers
8.0 Amp 100 Volt
ECCN:EAR99 16 16 0.970 15.52
3 1
512-ISL9R8120P2
Fairchild Power Diodes
8A 1200V STEALTH
ECCN:EAR99 8 8 1.600 12.80
4 1
647-UKW1C221MED
Nichicon Audio Electrolytic Capacitors
220uF 16V
ECCN:EAR99 2 2 0.170 0.34

 

[Mush]

Thanks Phi70! I going to order the parts.

I just checked my notes and the Liang 10vac filament taps are at 4.5amps. If they are like old American stuff, they will have been overbuilt by at least 20%. The Liang is overbuilt in general so I am going to assume that it can supply enough current for 813 tubes. If anyone has any comments, I'd greatly appreciate it.

 

[phi70]

Not sure if I agree re: overbuilt

Note that I boosted the B+ filtering value way way up from 200uF to 390uF.
Since there is no tube rectification and I am using fairchild Hexfreds there's no fear of rectifier arcing. The diodes really made a difference in lowering the noise floor.
Also the red cathode resistors were the ones that failed causing the previous owner to be royally confused about biasing after he hacked with it and almost destroyed it.
Upgrade the resistors to Mills non inductive wirewound, also upgrade those
whatever EA or AE coupling caps to anything decent.
I think this way you max out the capabilities of the orig design without
venturing into new tube territory which may stress-test the trannies and other parts of the circuit.
Good luck and have fun.

 

[phi70]

BTW that 200uF x 3 was in series

So 845 B+ filtering was a measly 70uF shared between 2 channels at best.

 

[phi70]

Speakin of the devil

Same seller who sold me the electrically hazardous L845 is selling another unit on EB. Note how the input wires were changed but stripped BARE laying right on top of the 845 socket (!!!!) and how the input RCAs were mutilated. Looks like the 300B sockets were hacked too just like the unit he sold me.

 

[michg365]

Recommended Upgrades

I just purchased a Mr Liang LS-845-3 (with 845 / 300B tubes). Having read through this thread 3 times, I am still confused. My question is what would be the best modifications (if any) to take the amp to take it to the next level. I am good with a soldering iron but not a tech. So I am hoping for a simple list of upgrades from people who have modified there amp with good results. I would prefer to keep the same basic design and not completely change the amp. Any suggestions would be appreciated and I hope would help others also. Thanks in advance.

 

[zcables]

I just purchased a Mr Liang LS-845-3 (with 845 / 300B tubes). Having read through this thread 3 times, I am still confused. My question is what would be the best modifications (if any) to take the amp to take it to the next level. I am good with a soldering iron but not a tech. So I am hoping for a simple list of upgrades from people who have modified there amp with good results. I would prefer to keep the same basic design and not completely change the amp. Any suggestions would be appreciated and I hope would help others also. Thanks in advance.

I second that as I just picked up a LS-845-5 with 845/300B/6Ж4.

Bump

 

[phi70]

Don't try this at home

If you are just solder-handy but not tube-amp handy please dont try it at home.

1000+V raw B+ on the Mr. Liang can fry you in a split second.

The "safer mods" would be to just replace all the small diodes with fairchild Hexfreds (1200V 8A)
and large diodes with ST Schottky's (100V 8A/12A)
and replace those whatever EA AE coupling caps with your favorite.

The lytic caps involve flipping the board and if you destroy the socket/s
by damaging the vias as you pull out the old cap it might take a long time to troubleshoot and troubleshooting that section can be very DANGEROUS.

 

[zcables]

Thank you for the quick reply and I am handy with electronics as well as HV tube amps.

Coupling caps was going to be my first mod, so I'll take that advice to heart. Which coupling caps did you replace?

If you're suggesting replacing the electrolytic caps, are you also suggesting that the stock power supply filtering is inadequate or underrated?

Thank you for your help and suggestions phi70.