mr liang
Hi
Nice 845 schematic on Hashimoto web site.Looks pretty simple.I have tried both versions of liang mods on lampizator site but didnt find any improvement over standard circuit.Finally removed 845 tubes ,fitted gm70 tubes and bigger heater supply,can now use with cheapish Russian tubes and I think it sounds better.
Regards Dave.
Hi
Nice 845 schematic on Hashimoto web site.Looks pretty simple.I have tried both versions of liang mods on lampizator site but didnt find any improvement over standard circuit.Finally removed 845 tubes ,fitted gm70 tubes and bigger heater supply,can now use with cheapish Russian tubes and I think it sounds better.
Regards Dave.
volume pot is the least of your worries
Overall I think that without the upgrade the unit sounds like a pile of trash.
After the upgrade its worth listening to but application is very very limited to high efficiency speakers.
Also look at the resistors wiring the 845 painted red... what a joke... the call it "red firecracker" in the chinese brochure...some communist propaganda??... If you want good sound change them to Caddock....
Overall I think that without the upgrade the unit sounds like a pile of trash.
After the upgrade its worth listening to but application is very very limited to high efficiency speakers.
Also look at the resistors wiring the 845 painted red... what a joke... the call it "red firecracker" in the chinese brochure...some communist propaganda??... If you want good sound change them to Caddock....
I fired the amp up last night after electrical testing, and the sound quality was not bad. The bass was thin and the soundstage seemed a little flat, but vocals were good, although not overly musical.
Everything seemed to work well electrically, and I opened it up to find no defects in the production or assembly. The two transformers closest to the front however did run VERY hot after a few hours, too hot to touch.
I am still going to give the amp some time to settle down and open up as it only has about 2-3 hours on the tubes and components.
Everything seemed to work well electrically, and I opened it up to find no defects in the production or assembly. The two transformers closest to the front however did run VERY hot after a few hours, too hot to touch.
I am still going to give the amp some time to settle down and open up as it only has about 2-3 hours on the tubes and components.
Here is the schematic which was sent with my amp if anyone has any comments.
An externally hosted image should be here but it was not working when we last tested it.
With some initial burn-in complete, but sound quality is decent, but the bass is shy; more so than my 300B amp which shouldn't be happening.
Does anyone have any circuit mods/tweaks I can try to improve the bottom end of the amp? I'm going to be replacing the coupling caps, diodes, "fire cracker resistors", and probably power supply caps, but I doubt that will address a lean bottom end.
Does anyone have any circuit mods/tweaks I can try to improve the bottom end of the amp? I'm going to be replacing the coupling caps, diodes, "fire cracker resistors", and probably power supply caps, but I doubt that will address a lean bottom end.
I measure the resistance across the binding posts on the LS-845 amp this morning and it measured 1ohm from 8ohm post to ground post, and .8ohm from 4ohm post to ground post; both sides. I then measured the resistance across the binding posts on my SET 300B amp this morning and it measured .4ohm from 8ohm post to ground post, and .3ohm from 4ohm post to ground post; both sides.
Obviously, this is less than half the resistance across the output transformer taps, but could that be causing the issue?
Obviously, this is less than half the resistance across the output transformer taps, but could that be causing the issue?
Might upgrading the filter caps to a higher value also improve the bass response?
In days of yore (in this case yore is before 1970), amplifier designers, mostly due to cost constraints, calculated the "minimum decoupling" value, (meaning how small of a capacitor they could get away with) when specifying filter capacitor values. Later, it was discovered that using capacitors of a much higher value, particularly directly attached to the center-tap of the output transformer (thus the least amount of impedance between it and the output tubes), could improve perceived bass response and transient overload recovery. Thus in almost every case larger filter capacitors than those specified on the diagrams results in an improvement in sound quality.
Update:
I recently received a pair a 6J4P/6AC7GT glass-body tubes to replace the stock 6Ж4 tubes. I got them because I don't like the look of metal tubes, but after popping them in, the bass response improved in the amp to where it should be. The new tubes only have about an hour on them, so they need lots of burn-in time, but the sound so far is impressive and much improved. Any thoughts?
I recently received a pair a 6J4P/6AC7GT glass-body tubes to replace the stock 6Ж4 tubes. I got them because I don't like the look of metal tubes, but after popping them in, the bass response improved in the amp to where it should be. The new tubes only have about an hour on them, so they need lots of burn-in time, but the sound so far is impressive and much improved. Any thoughts?
Yup, I do tend to agree....
The only way heat can escape a valve is by radiation heating the glass and then by convection of air...
REflecting the heat Back to the valve will mean for a hotter and possibly shorter life of the valve...
I read a very interesting pdf recommended by someone here called 'Getting the most from Vacuum Tubes'
--It was quite particular in the fact that Heat is one of the biggest factors determining valve life....
No surprise really if you think about it--The bulb that burns twice as bright--lasts half as long....
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