The relay is for triode/pentode switching.
The contacts can burn or stick together if the relay is operated with music playing.
Relay type: TAKAMISAWA (Fujitsu) RY5W-K
I propose to unsolder and check this one.
--
The reason for the burnt cathode and screen resistors is most likely either defect tube (shorted) , or missing bias supply.
When you have replaced the burnt resistors again, turn on the amp without KT88 tubes in this channel, and measure the grid voltage (pin 5). It should be about -50 to -60 volt.
Normally the kathode resistors are small wattage so that they burn out if something is wrong. I see you have replaced with big ones.
SveinB
The contacts can burn or stick together if the relay is operated with music playing.
Relay type: TAKAMISAWA (Fujitsu) RY5W-K
I propose to unsolder and check this one.
--
The reason for the burnt cathode and screen resistors is most likely either defect tube (shorted) , or missing bias supply.
When you have replaced the burnt resistors again, turn on the amp without KT88 tubes in this channel, and measure the grid voltage (pin 5). It should be about -50 to -60 volt.
Normally the kathode resistors are small wattage so that they burn out if something is wrong. I see you have replaced with big ones.
SveinB
Attachments
Last edited:
I would not pay more than what a set of transformers are worth, even that is probably too much. I have one, and am stripping it for parts. The OPT's on my amp were wound with 12K plate to plate impedance. I think there are much better ways of spending your money. That's just my opinion, no more no less.
Well. We have changed the deal. I swap my HK3490 amplifier for his MA and i stand for the shipping costs for both of us. So, it gets quite cheaper.
So, what's the real problem with that amp? I am new to this so please explain
For some reason, two of my recent replies to 'Rullknufs' seem to have been removed. I cannot think that they contravened any forum rules, if so, it was unintentional, but basically I explained that all the information I have on Music Angel Amplifiers came from this site in the first place(most can be found in the posts on these 3 pages). It's been about four years since I repaired/modified an XD-SE(the KT88 version)for forum member
'jesabel', who, AT THAT TIME, had paid £165 for one from eBay(£300 inc. shipping & UK import duty) Details of the various substitutions and modifications I made to his amplifier can be found in a thread headed 'Music angel amps', started on 01-01-2007, so I won't
repeat them. Suffice it to say that a fair amount of work, and quite a few component changes were needed, mainly due to a fault having developed where C25 and some 1N4007s had failed.
Rereading the posts by 'jesabel', his opinion of the XD-SE, his opinion was that 'it was quite stunning', and 'a massive improvement in clarity and stereo separation over a combination of Audiolab 8000 & Rotel RB850 '(This was BEFORE I had repaired & modified
his amp., and I have to say that I was quite impressed by it's performance, even into
a pair of old 'mid-fi' speakers I use in my workshop for test purposes.(This was meant to be a 'quick reply!!!)
As an aside, no doubt others will have seen various errors in some of the schematics-e.g., the cathode resistor for the long tail pair stage of the EL34 amp is
shown as being 3K, with 111v across it. This would be 37mA, and require a 5 Watt resistor. I feel sure that the correct value for this R is 39 or 43KOhms, which equals
ca.2.6mA, This figure ties in with the anode(plate)voltages and load resistor values
shown. Incidentally I'm puzzled by the sometimes non-standard values encounterd
in Chinese made equipment, often not even in the E24 series.
'jesabel', who, AT THAT TIME, had paid £165 for one from eBay(£300 inc. shipping & UK import duty) Details of the various substitutions and modifications I made to his amplifier can be found in a thread headed 'Music angel amps', started on 01-01-2007, so I won't
repeat them. Suffice it to say that a fair amount of work, and quite a few component changes were needed, mainly due to a fault having developed where C25 and some 1N4007s had failed.
Rereading the posts by 'jesabel', his opinion of the XD-SE, his opinion was that 'it was quite stunning', and 'a massive improvement in clarity and stereo separation over a combination of Audiolab 8000 & Rotel RB850 '(This was BEFORE I had repaired & modified
his amp., and I have to say that I was quite impressed by it's performance, even into
a pair of old 'mid-fi' speakers I use in my workshop for test purposes.(This was meant to be a 'quick reply!!!)
As an aside, no doubt others will have seen various errors in some of the schematics-e.g., the cathode resistor for the long tail pair stage of the EL34 amp is
shown as being 3K, with 111v across it. This would be 37mA, and require a 5 Watt resistor. I feel sure that the correct value for this R is 39 or 43KOhms, which equals
ca.2.6mA, This figure ties in with the anode(plate)voltages and load resistor values
shown. Incidentally I'm puzzled by the sometimes non-standard values encounterd
in Chinese made equipment, often not even in the E24 series.
If you are buying(subject to parental permission!)a M.A. XD-800MKIII or similar(with 2 x KT88 output valves), you may want to carry out some, or all , of the mods. which I did to
the one I repaired back in early 2007, details of which are in several posts I placed on this forum at the time, together with various comments and suggestions by other members. The main things to do are to replace any 1n4007 and 1n5407 diodes with the equivalent 'Ultrafast'(UF)versions, and use higher value electrolytics to replace the various smoothing capacitors. Other mods. may be desirable in some cases
The easiest way to access previous posts is to go to 'Community'(at the top of the page),and select 'Members List'. From there you can find any post by any member over quite a number of years.
the one I repaired back in early 2007, details of which are in several posts I placed on this forum at the time, together with various comments and suggestions by other members. The main things to do are to replace any 1n4007 and 1n5407 diodes with the equivalent 'Ultrafast'(UF)versions, and use higher value electrolytics to replace the various smoothing capacitors. Other mods. may be desirable in some cases
The easiest way to access previous posts is to go to 'Community'(at the top of the page),and select 'Members List'. From there you can find any post by any member over quite a number of years.
Yes, indeed you can.
Until you have the knowledge and skills, that may actually be the best strategy. You may consider spending a little money on some good small signal tubes to try.
The mod you should do however, is to connect the safety earth from the power input connector to chassis. This is often missing.
Svein.
What tubes should i get then?
I will calculate some costs for the KT88 one.
How do i connect the safety earth to the chassis?
As Svein has said, you can use the 800MKIII in it's unmodified form until you have the ability and funds to modify it. The various mods. are intended to improve it's performance. I hope you don't mind me pointing out that, like all valve
equipment, (very)high voltages are present within the amplifier(The main H.T.{B+}for instance, is over 400vDC), and GREAT CARE is needed when working on such things. Electrolytic Capacitors hold a charge for a long while after the (mains) power is switched off. Having said that, it is quite easy to fit a mains earth if one isn't already present. A multimeter can be used to check whether the center pin of the 3-pole mains inlet is connected to the amp's metalwork. If not, remove the bottom cover and solder a short length of insulated wire(green & yellow is the standard color in the U.K.) to the center pin. Fit a suitable spade or eyelet connector to the other end of this wire, fastening this to chassis via one of the existing fixing bolts There is one about 1"(25mm)
away from the mains socket. A shakeproof washer should be used under the nut(one should already be present).
equipment, (very)high voltages are present within the amplifier(The main H.T.{B+}for instance, is over 400vDC), and GREAT CARE is needed when working on such things. Electrolytic Capacitors hold a charge for a long while after the (mains) power is switched off. Having said that, it is quite easy to fit a mains earth if one isn't already present. A multimeter can be used to check whether the center pin of the 3-pole mains inlet is connected to the amp's metalwork. If not, remove the bottom cover and solder a short length of insulated wire(green & yellow is the standard color in the U.K.) to the center pin. Fit a suitable spade or eyelet connector to the other end of this wire, fastening this to chassis via one of the existing fixing bolts There is one about 1"(25mm)
away from the mains socket. A shakeproof washer should be used under the nut(one should already be present).
Ah, that mod sounds like a suitable difficulty for me
I've heard that tube amps are dangerous to work with. What about waiting 5 minutes from power off to opening them up? And keep one hand in my pocket and work with the other?
Both suggestions are good advice, Rullknufs, as any experienced service engineer will tell
you. Large value Electrolytics can hold their charge for longer than 5 minutes. They can be discharged, once the equipment is switched off, by connecting the red(+)lead of a multimeter(set on a high DC Volts range) to the capacitor's +ve terminal, and the meter's black(-ve) lead to the amp's chassis. An analogue meter is best for this. As the meter reading falls, switch it to lower ranges until a reading of (close to)zero volts is shown.
The capacitor will then be discharged to a safe level. (It goes without saying, I hope, that Insulated test leads, probes, and clips MUST be used when working on High Votage
items.)
(P.S. -Enjoy being 15. The years will fly past fast enough!!!)
you. Large value Electrolytics can hold their charge for longer than 5 minutes. They can be discharged, once the equipment is switched off, by connecting the red(+)lead of a multimeter(set on a high DC Volts range) to the capacitor's +ve terminal, and the meter's black(-ve) lead to the amp's chassis. An analogue meter is best for this. As the meter reading falls, switch it to lower ranges until a reading of (close to)zero volts is shown.
The capacitor will then be discharged to a safe level. (It goes without saying, I hope, that Insulated test leads, probes, and clips MUST be used when working on High Votage
items.)
(P.S. -Enjoy being 15. The years will fly past fast enough!!!)
Uhm, i don't think 6W is enough.
The driver's sensibility is 86db/1w/1m. I guess the box adds a little to that aswell.
It is crossed over at around 100Hz, so there's not much bass going into the driver.
But, i like to play loud (as loud as i can without destroying the speakers) so i'm not sure if 6W will be enough or not.
The driver's sensibility is 86db/1w/1m. I guess the box adds a little to that aswell.
It is crossed over at around 100Hz, so there's not much bass going into the driver.
But, i like to play loud (as loud as i can without destroying the speakers) so i'm not sure if 6W will be enough or not.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.