Re bias on the 845 tube
Hi Ali et al
Now correct me if I am wrong but if the tube was running at those levels it would be well over its specified ratings and would not last for long.....
There might be only 820 volts on your anode supply but is that measure across the plate and one of the filament leads? This is the only accurate way to really set the bias...if there is 820 volts on the supply you set the bias for the rated 100watt dissipation...
Can we all measure our plate volts in such a way and come back with the results....the other way to set the correct bias is in the cathode side of the 845...this does not tell you what the operating volts of the 845 plate is?
In such tubes as this with a high supply voltage I would rather work in the cathode side of the supply....with my hands well out of the amp.....
Any Ideas on how long it takes for the HT to come off the supply rails on this amp....?
As for the sound of the amp I for one think it is excellent...there is room for improvement from what I have read about capacitor upgrades....
As for my sound sources: Garrard 401, SME 3009 MK2, Pioneer PN4MC high output moving coil, Rotel RQ970BXII Phono stage, Marantz CD67SE CD, several reel to reel tape machines pro and semi pro....and the other input receives input from digital cable tv box, dvd recorder and video....most of the day the radio is on BBC of course through cable box...hence the reference to digital sounding better through the amp....
Oh best source by far vinyl...followed by CD and then cable...of course when you get to cable tv the sound is as good as the sourse or the original recording and a lot of it is severly limited in it's responce........but most modern programming from tv is of an excellent sound quality even if the progamming itself can leave a little to be desire these days....
oh speakers nearly forgot vintage late 60s things by Dynastatic...which uses 12" Richard Allen Bass/mids and Shackman Electrostatic top end.....they can sound lean but mostly they reflect the source more accurately...suit me and they can produce gut rending bass if it is there they add nothing....
thanks
steve in the UK
Hi Ali et al
Now correct me if I am wrong but if the tube was running at those levels it would be well over its specified ratings and would not last for long.....
There might be only 820 volts on your anode supply but is that measure across the plate and one of the filament leads? This is the only accurate way to really set the bias...if there is 820 volts on the supply you set the bias for the rated 100watt dissipation...
Can we all measure our plate volts in such a way and come back with the results....the other way to set the correct bias is in the cathode side of the 845...this does not tell you what the operating volts of the 845 plate is?
In such tubes as this with a high supply voltage I would rather work in the cathode side of the supply....with my hands well out of the amp.....
Any Ideas on how long it takes for the HT to come off the supply rails on this amp....?
As for the sound of the amp I for one think it is excellent...there is room for improvement from what I have read about capacitor upgrades....
As for my sound sources: Garrard 401, SME 3009 MK2, Pioneer PN4MC high output moving coil, Rotel RQ970BXII Phono stage, Marantz CD67SE CD, several reel to reel tape machines pro and semi pro....and the other input receives input from digital cable tv box, dvd recorder and video....most of the day the radio is on BBC of course through cable box...hence the reference to digital sounding better through the amp....
Oh best source by far vinyl...followed by CD and then cable...of course when you get to cable tv the sound is as good as the sourse or the original recording and a lot of it is severly limited in it's responce........but most modern programming from tv is of an excellent sound quality even if the progamming itself can leave a little to be desire these days....
oh speakers nearly forgot vintage late 60s things by Dynastatic...which uses 12" Richard Allen Bass/mids and Shackman Electrostatic top end.....they can sound lean but mostly they reflect the source more accurately...suit me and they can produce gut rending bass if it is there they add nothing....
thanks
steve in the UK
Where can you buy it?
Hi well it is usually listed on ebay try searching under Mr'liung it is currently not listed but keep trying, it will turn up again and I must say that mine arrived safely with not dents or dint or bent chassis....just a few scratches around about where the tube cage had come out in transit....
It is an amazing piece of kit and it now seems it does benefit from the odd tweak here and there ....more of that will follow by others more experienced than myself....but I am going to be upgrading a few of the components shortly...
Steve in the UK
Hi well it is usually listed on ebay try searching under Mr'liung it is currently not listed but keep trying, it will turn up again and I must say that mine arrived safely with not dents or dint or bent chassis....just a few scratches around about where the tube cage had come out in transit....
It is an amazing piece of kit and it now seems it does benefit from the odd tweak here and there ....more of that will follow by others more experienced than myself....but I am going to be upgrading a few of the components shortly...
Steve in the UK
Re: Where can you buy it?
Yes, my top plate had a few scratches were the tube cage jumped out in transit. Best to ask them not ship that tube cage if you don't need it. Causes more damage than its worth.
That front ali top plate unscrews and it looks ok underneath to me, brush stainless but with some extra holes.
Best upgrade by far for my system was those 0.22uF 600V and 0.47uF 600V caps on the front pcb. Me and a freind got some copper body obbligatto off brian at diyhifisupply.com, they are cheap and good quality film caps. Miles more open and transparent. Also those JJ tesla tubes are very good, extended and very sweet sounding.
I did not like the RCA 6js7 but maybe operating point is wrong in this amp for that tube as mentioned. RCA 5693 maybe a better match ??
Amp is a great bit of kit for the price.
Stevie342000 said:
Yes, my top plate had a few scratches were the tube cage jumped out in transit. Best to ask them not ship that tube cage if you don't need it. Causes more damage than its worth.
That front ali top plate unscrews and it looks ok underneath to me, brush stainless but with some extra holes.
Best upgrade by far for my system was those 0.22uF 600V and 0.47uF 600V caps on the front pcb. Me and a freind got some copper body obbligatto off brian at diyhifisupply.com, they are cheap and good quality film caps. Miles more open and transparent. Also those JJ tesla tubes are very good, extended and very sweet sounding.
I did not like the RCA 6js7 but maybe operating point is wrong in this amp for that tube as mentioned. RCA 5693 maybe a better match ??
Amp is a great bit of kit for the price.
Re Mr Liang & Obligato Capacitors
Hi
Thanks for that link to Diy Hifi supply....will check out the other others you were not wrong on the reasonable price on the capacitors I could not get all copper had to get the 0.22uFs in black body copper bodies were out of stock....but got the copper bodies for the 0.47uF capacitors, they certainly look the part in black or copper body ...where as the styling in Jensen capacitors is more like the Hunts old style....
Needless to say given the more than excellent exchange rate we are getting with the US $ at the minute I verily did snap them up.....
So it looks like I will shortly be replacing those capacitors and calibrating those meters as in earlier posts.....
TTFN
Steve in the UK
ps as for the metal tube cage it did serve a purpose it protected the fragile tubes in transit.....
Hi
Thanks for that link to Diy Hifi supply....will check out the other others you were not wrong on the reasonable price on the capacitors I could not get all copper had to get the 0.22uFs in black body copper bodies were out of stock....but got the copper bodies for the 0.47uF capacitors, they certainly look the part in black or copper body ...where as the styling in Jensen capacitors is more like the Hunts old style....
Needless to say given the more than excellent exchange rate we are getting with the US $ at the minute I verily did snap them up.....
So it looks like I will shortly be replacing those capacitors and calibrating those meters as in earlier posts.....
TTFN
Steve in the UK
ps as for the metal tube cage it did serve a purpose it protected the fragile tubes in transit.....
In that case if you want them to ship the cage ask them to open the box and tape it down onto the amp so it cannot move and scratch the top plate.
On another subject....
Does anyone know if it is possible to fit a grid choke or ultrapath cap to this design ? Ultrapath would be cheap and it made quite an improvement on my previous 300B SET amp
On another subject....
Does anyone know if it is possible to fit a grid choke or ultrapath cap to this design ? Ultrapath would be cheap and it made quite an improvement on my previous 300B SET amp
Re location
Hi Swamp Thing
That is well spooky.....but interesting now should I need a willing volunteer to stick their fingers in this thing...I am sort of scared of those plate volts and rightly so....but we should not forget the mains supply can bite severly too......
I take it given your directions in the last post that you live in or near Bolton/Wigan area? I am Salford city centre end.....
Have we spoken off group? Not sure if we have, have so many contacts that even I get confused....
I tend to loose the threads on these forums as well or as to who said what...this one is getting quite long now and has had a far few viewings as well.....
I got into a little trouble with some of the other members earlier on in this posting as this was a DIY group and I was discussing a pre built ready made amp......
The purpose is now bearing fruit others more foolish or knowledgeable than myself ...have willingly stuck their hands inside this thing and now we are starting to get feedback on improvements which to me is a function of a DIY Forum.....
I ordered some of the Obligato capacitors and they should be mailed out tomorrow and the other thing I need to do with mine is to calibrate the meter......
One other thing I have noted on mine is that the transformer cage runs hot over those mains transformers....have others noted this? Or is it me?
catch you later
Steve
Hi Swamp Thing
That is well spooky.....but interesting now should I need a willing volunteer to stick their fingers in this thing...I am sort of scared of those plate volts and rightly so....but we should not forget the mains supply can bite severly too......
I take it given your directions in the last post that you live in or near Bolton/Wigan area? I am Salford city centre end.....
Have we spoken off group? Not sure if we have, have so many contacts that even I get confused....
I tend to loose the threads on these forums as well or as to who said what...this one is getting quite long now and has had a far few viewings as well.....
I got into a little trouble with some of the other members earlier on in this posting as this was a DIY group and I was discussing a pre built ready made amp......
The purpose is now bearing fruit others more foolish or knowledgeable than myself ...have willingly stuck their hands inside this thing and now we are starting to get feedback on improvements which to me is a function of a DIY Forum.....
I ordered some of the Obligato capacitors and they should be mailed out tomorrow and the other thing I need to do with mine is to calibrate the meter......
One other thing I have noted on mine is that the transformer cage runs hot over those mains transformers....have others noted this? Or is it me?
catch you later
Steve
Re: Re location
I have had the amp on with tubes and the bottom cover off to help a friend find a fault on his amp but I certainly don't poke around with scope or meter probes. Clip them on first then stand well back then switch on. Sometimes best to unplug the 800V HT at the back of the psu pcb if you don't need it. The mains switch is a pain, it is just in a nice position were you could catch it... well rather the mains than the big HT I guess. I think this thing could kill. Be careful.
I think we spoke by email maybe off forum ?? I get mixed up. I am about 20 mins from salfold just off the A580. V Spooky
As for the diy only thing, I thought modding an amp was classed as diy so it should be ok with the moderators.
Yes that cage does get hot due to the heat off the 845's. My friend is making a heat shield. I'll report back if he does with some pictures. Might be a worthwhile addition. I think there is scope for many tweaks in this amp.
Stevie342000 said:
I have had the amp on with tubes and the bottom cover off to help a friend find a fault on his amp but I certainly don't poke around with scope or meter probes. Clip them on first then stand well back then switch on. Sometimes best to unplug the 800V HT at the back of the psu pcb if you don't need it. The mains switch is a pain, it is just in a nice position were you could catch it... well rather the mains than the big HT I guess. I think this thing could kill. Be careful.
I think we spoke by email maybe off forum ?? I get mixed up. I am about 20 mins from salfold just off the A580. V Spooky
As for the diy only thing, I thought modding an amp was classed as diy so it should be ok with the moderators.
Yes that cage does get hot due to the heat off the 845's. My friend is making a heat shield. I'll report back if he does with some pictures. Might be a worthwhile addition. I think there is scope for many tweaks in this amp.
re Hot transformers
Hi Swampy
I am just abou to botch something up with two layers of cardboard with a thin stip of polystyrene in between and with some aluminium foil wrapped around the whole lot....I had figured it was the 845s and it varies with weather as to how hot it gets thank goodness we have not had a 30 C+ summer....it would be straining I think....of course the other option is to get a small fan for cooling that area...
Do you have an idea of how long I should turn this thing off for before I put my hand inside to change those capacitors....of course I will start off by taking out the 845 HT......
Yes it was fine with moderators as this was the first thing I had posted on and the moderators were checking what I said before I was free to say whatever I wanted to in posts...but some people are real touchy......especially the purists.....but if your looking for information on a amp or a subject what better place to come than a diy audio forum...such as this.....
I will investigate both and report back.....
catch you later
Steve
ps yes we did talk off group I checked your profile.....
Hi Swampy
I am just abou to botch something up with two layers of cardboard with a thin stip of polystyrene in between and with some aluminium foil wrapped around the whole lot....I had figured it was the 845s and it varies with weather as to how hot it gets thank goodness we have not had a 30 C+ summer....it would be straining I think....of course the other option is to get a small fan for cooling that area...
Do you have an idea of how long I should turn this thing off for before I put my hand inside to change those capacitors....of course I will start off by taking out the 845 HT......
Yes it was fine with moderators as this was the first thing I had posted on and the moderators were checking what I said before I was free to say whatever I wanted to in posts...but some people are real touchy......especially the purists.....but if your looking for information on a amp or a subject what better place to come than a diy audio forum...such as this.....
I will investigate both and report back.....
catch you later
Steve
ps yes we did talk off group I checked your profile.....
re heat reflector
Hi All
I am sure I am not the only one who thinks that that transformer cage although it is acting as a heatsink is running those transformers too hot mine are the toroidal ones so I am doubly aware of this as they do not have the large cores of the EI transformers and I suspect can not cool as quickly...
I tried to make up my own heat reflecter....I started off with a the sandwich approach of two pieces of carboard with a small thin polystyrene layer with it all wrapped up in aluminium foil.....
This turned out to be too thick and there was not much clearance between this and the output tubes...so I cut out the polystyrene...this seems to be doing the job the transformer cage is running much cooler now and have decided to cut it down futher and now it is just a single layer of cardboard which makes it thinner and less likely for the cardboard to spontaneously combust which it might given the heat given off by these tubes this is not meant as a permanent measure....
However thinking a little more laterally you could use ordinary ceramic tiles a la kitchen or bathroom which would not combust...it needs further work but it is a start....
Catch you all later
steve
Hi All
I am sure I am not the only one who thinks that that transformer cage although it is acting as a heatsink is running those transformers too hot mine are the toroidal ones so I am doubly aware of this as they do not have the large cores of the EI transformers and I suspect can not cool as quickly...
I tried to make up my own heat reflecter....I started off with a the sandwich approach of two pieces of carboard with a small thin polystyrene layer with it all wrapped up in aluminium foil.....
This turned out to be too thick and there was not much clearance between this and the output tubes...so I cut out the polystyrene...this seems to be doing the job the transformer cage is running much cooler now and have decided to cut it down futher and now it is just a single layer of cardboard which makes it thinner and less likely for the cardboard to spontaneously combust which it might given the heat given off by these tubes this is not meant as a permanent measure....
However thinking a little more laterally you could use ordinary ceramic tiles a la kitchen or bathroom which would not combust...it needs further work but it is a start....
Catch you all later
steve
Re: re Hot transformers
Not really but not long. Switch off with music playing and it all dies away after a few seconds. By the time you open it up it everything should have all discharged. According to the circuit the main psu caps have bleed / balance resistors across them.
There are 2 ways to change those film caps.
Quick and dirty method... cut the old caps out close to the body leaving the legs poking through. Bend them over slightly to stop them dropping through when you solder onto them. They now act like vero pins and you can just solder on top without taking the board out. Nice and easy. My friend did this.
Proper method... remove the front pcb and solder in both sides. I did this method. Well, not fully removed but I got to the stage were I could just tilt the pcb up to get to the otherside and solder them in.
Stevie342000 said:
Not really but not long. Switch off with music playing and it all dies away after a few seconds. By the time you open it up it everything should have all discharged. According to the circuit the main psu caps have bleed / balance resistors across them.
There are 2 ways to change those film caps.
Quick and dirty method... cut the old caps out close to the body leaving the legs poking through. Bend them over slightly to stop them dropping through when you solder onto them. They now act like vero pins and you can just solder on top without taking the board out. Nice and easy. My friend did this.
Proper method... remove the front pcb and solder in both sides. I did this method. Well, not fully removed but I got to the stage were I could just tilt the pcb up to get to the otherside and solder them in.
Re heat and reduction of
Hi Swamp
Well I just nearly did my back in lifting the amp off the floor where it has sat since arrival but purely for that reason....it is just too big and heavy to move...I nearly dropped it but new I had to move my hands back towards the transformers to balance it out.....unfortunately I had it a foot or so above floor so could not move too rapidly.....
It should keep it cooler as it is off the floor...I have put the tube cage back on which should take some of that heat of the transformer cage and the transformers.....I have a feeling although I prefer it with the tube cage off that is acts as a heatsink and helps to radiate the heat away from other parts of the amp......
I have noticed that the tube cage is a little dented in places and could do with a bash to flatten it back out.....needless to say it sounds wonderfully open....lots of detail for top to bottom....love the way the notes hang in the air......
It does not matter what sort of music you throw at this amp it just romps through it and plays everything well...need to find something complicated...loves those RCA Living Stereo or Mercury Living Presence, UK Decca, 50/60's EMI stuff too sounds great.....even Callas sounds less harsh and you can see her artistry shining through....
I just love it...and what it does....it does it so well....
catch you later
steve
Hi Swamp
Well I just nearly did my back in lifting the amp off the floor where it has sat since arrival but purely for that reason....it is just too big and heavy to move...I nearly dropped it but new I had to move my hands back towards the transformers to balance it out.....unfortunately I had it a foot or so above floor so could not move too rapidly.....
It should keep it cooler as it is off the floor...I have put the tube cage back on which should take some of that heat of the transformer cage and the transformers.....I have a feeling although I prefer it with the tube cage off that is acts as a heatsink and helps to radiate the heat away from other parts of the amp......
I have noticed that the tube cage is a little dented in places and could do with a bash to flatten it back out.....needless to say it sounds wonderfully open....lots of detail for top to bottom....love the way the notes hang in the air......
It does not matter what sort of music you throw at this amp it just romps through it and plays everything well...need to find something complicated...loves those RCA Living Stereo or Mercury Living Presence, UK Decca, 50/60's EMI stuff too sounds great.....even Callas sounds less harsh and you can see her artistry shining through....
I just love it...and what it does....it does it so well....
catch you later
steve
Hi All,
Yes I've noticed too how hot the transformer cage gets.Can't be good for them long-term.Was thinking of what I think Unison Research did on their 845 or 211 can't remember the particular amp but they have shields around the valves made from some sort of metal tubing cut lenthways then across on the top and bottom.Upshot is there is a shield behind the power valves to keep heat away from the rest of the amp.Effective and looks nice too.Just need to find some Aly. tubing and someone with a bandsaw.
Regards,Ali
Yes I've noticed too how hot the transformer cage gets.Can't be good for them long-term.Was thinking of what I think Unison Research did on their 845 or 211 can't remember the particular amp but they have shields around the valves made from some sort of metal tubing cut lenthways then across on the top and bottom.Upshot is there is a shield behind the power valves to keep heat away from the rest of the amp.Effective and looks nice too.Just need to find some Aly. tubing and someone with a bandsaw.
Regards,Ali
A friend has just got some stainless sheet cut to size and he got me a piece today. I am now making a 'thermionic heatshield' In other words just spraying it black and trying not to make a mess of it.
It was unison research 845 that had the ali sheild. That amp was on eBay a month ago. Some large diameter ali tubing cut in the middle lengthways would be ideal and look good.
In other words just spraying it black and trying not to make a mess of it.It was unison research 845 that had the ali sheild. That amp was on eBay a month ago. Some large diameter ali tubing cut in the middle lengthways would be ideal and look good.
Re Mr Liang Heat Shield
Hi Swamp, Ali et al
Just to re-cap for you Unison research made their heatshield out of ceramic...there was on of their 845 models on ebay last week I think.....it was wonderfully sculptured ........
Not sure you should paint it black you want it to reflect the heat not attract it....I have put the cage back on mine and have small fan near the transformer cage and with a piece of cardboard between the two cages wrapped in aluminium...that seems to be keeping things cooler....
Will try to pop to Topps tiles tomorrow to see if I can get some free samples and will try a couple of small white ceramic tiles between the two cage instead...should do the trick too...
Will keep you posted......
Catch you later
steve in the UK
Hi Swamp, Ali et al
Just to re-cap for you Unison research made their heatshield out of ceramic...there was on of their 845 models on ebay last week I think.....it was wonderfully sculptured ........
Not sure you should paint it black you want it to reflect the heat not attract it....I have put the cage back on mine and have small fan near the transformer cage and with a piece of cardboard between the two cages wrapped in aluminium...that seems to be keeping things cooler....
Will try to pop to Topps tiles tomorrow to see if I can get some free samples and will try a couple of small white ceramic tiles between the two cage instead...should do the trick too...
Will keep you posted......
Catch you later
steve in the UK
Re heat shield
Hi Ali
Your right it should be damn easy to make an aluminium or stainless heat shield ......would need to watch those sharp edges though....but should be easy enough to cut with some tin clippers or whatever...and then bend round into shape to form a chimney al la Unison Research....
Put me down for a couple of course the other option is to put a whisper fan inside transformer cage to help cooling.....just a thought
Steve in the UK
Hi Ali
Your right it should be damn easy to make an aluminium or stainless heat shield ......would need to watch those sharp edges though....but should be easy enough to cut with some tin clippers or whatever...and then bend round into shape to form a chimney al la Unison Research....
Put me down for a couple of course the other option is to put a whisper fan inside transformer cage to help cooling.....just a thought
Steve in the UK
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