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Ice-9 wrote:I usually replace cheap output valves with decent ones as soon as I get a new amp and bias it correctly. The left over cheap valves can be handy in your gig bag in case of a valve failure at a gig.

With all the trouble you have had DrNomis I would have been taking the amp back to the shop and asking for a new replacement amp, not a repair. We spend a lot of money on our gear and they should work out of the box without problems. Cheap valves I can accept but broken wires and non working parts is a sign the amp is used, either on display in the shop or another customers return. I have had a similar problem with an Fender EVH 5150 combo, It is now 7 months since I bought it and finally am getting a replacement, the thing is i'm still waiting for the replacement coming into stock and the shop asked me to return the original weeks ago as they have to be able to re sell it. (re sell it as new ! Remind me not to buy anything from this shop again).
Sorry to droll on a bit off topic, but my point is some music shops have bad business practices and you should of had a brand new replacement, I always check when unpacking things now weather they look like they have been re packed or looks used in any way.

EDIT- WOW, ive just found the Marshall MA100C amp is now available in the UK at £399. That is a good price for a 100w valve amp. Send yours back for a refund and buy a new one for half price (nearly).

I'd get it replaced with a brand new one except the warranty on it would be well and truly void by now, but yeah you do have a very good point there.....

Ice-9 wrote:.... the shop asked me to return the original weeks ago as they have to be able to re sell it. (re sell it as new ! Remind me not to buy anything from this shop again).

Too true.

I bought a channel strip (for use as a bass preamp wit a PA power amp, from Thomman, Germany), it was faulty when I got it (mains buzz on the balanced XLR output). The case had been opened, most of the screw heads were stripped and some screws missing. I would have sent it straight back but the fix was easy, I tightened the PCB grounding lead securing screw.

I get the impression that they just keep selling a unit until it doesn't come back.

The amp seems to have behaved itself since the last time I looked at it, hopefully it'll stay working....touchwood......

I recently bought a new Orange OR15 from a reputable internet website. The amp arrived with a buzzing noise. Turned out to be the effects loop tube. I replaced that tube and two days later an output tube blew, taking the fuse with it as well. I asked for a replacement amp at that time. Orange attempted to convince me to take the amp to an authorized repair center but I stood my ground and they sent me a new amp. Your story here is what really inspired me to stand my ground Dr Nomis-- Thank You.

bato001 wrote:I recently bought a new Orange OR15 from a reputable internet website. The amp arrived with a buzzing noise. Turned out to be the effects loop tube. I replaced that tube and two days later an output tube blew, taking the fuse with it as well. I asked for a replacement amp at that time. Orange attempted to convince me to take the amp to an authorized repair center but I stood my ground and they sent me a new amp. Your story here is what really inspired me to stand my ground Dr Nomis-- Thank You.

Ah, no worries at all mate, the main thing is that you got your Orange amp sorted, I'm still a bit mystified as to why my Marshall kept blowing main HT fuses all the time, I had a good look inside the amp and everything looked perfectly normal, as far as I could see I couldn't find any HT shorts to ground or anything else that would draw over 1A from the power supply, I'm starting to think that maybe one of the Sovtek 12AX7WA/7025 preamp valves I was using before might have been the cause of the trouble, since I've switched over to using two Chinese 12AX7B preamp valves as per bajaman's advice, so far I haven't had any problems.....touchwood......

since I've switched over to using two Chinese 12AX7B preamp valves

you won't have any more problems - those Sovtek /EHX tubes are the most unpredictable and worst emission tubes I have ever had the misfortune to have used
I would not be at all surprised if they were the cause of most of your problems Simon

bajaman wrote:

since I've switched over to using two Chinese 12AX7B preamp valves

you won't have any more problems - those Sovtek /EHX tubes are the most unpredictable and worst emission tubes I have ever had the misfortune to have used
I would not be at all surprised if they were the cause of most of your problems Simon

There's two ways I can think of that those Sovtek valves could have caused problems in my amp, one is that one of them could have had a cathode-to-heater leakage or short, the other is that one of them could have been oscillating at a very high frequency, I did notice that those Chinese 12AX7B valves made the amp sound better than it did with those Sovteks, funny thing is those Sovteks were practically brand new and sounded pretty gainy in my Baja Real Tube Overdrive pedal, I know, I really need to buy myself some kind of Valve testing equipment, anyway I'll keep you guys posted.......


Incidentally, the original preamp Valves (ECC83 types) sounded harsh and a bit unmusical hence the reason why I tried other preamp Valves in the first place.......


I am liking those Chinese 12AX7Bs though......

bajaman wrote:

since I've switched over to using two Chinese 12AX7B preamp valves

you won't have any more problems - those Sovtek /EHX tubes are the most unpredictable and worst emission tubes I have ever had the misfortune to have used
I would not be at all surprised if they were the cause of most of your problems Simon

Damn Bajaman, one of the first things I did when they sent me the replacement for the OR15 was swap out V1 from the JJ ECC83S to an EHX 12AX7 because the JJ sounded muddy to me.

What is a better replacement for the JJ to get the clarity without the possible problems of the EHX tube?

bato001 wrote:

bajaman wrote:

since I've switched over to using two Chinese 12AX7B preamp valves

you won't have any more problems - those Sovtek /EHX tubes are the most unpredictable and worst emission tubes I have ever had the misfortune to have used
I would not be at all surprised if they were the cause of most of your problems Simon

Damn Bajaman, one of the first things I did when they sent me the replacement for the OR15 was swap out V1 from the JJ ECC83S to an EHX 12AX7 because the JJ sounded muddy to me.

What is a better replacement for the JJ to get the clarity without the possible problems of the EHX tube?

Maybe try a Chinese 12AX7B, or maybe an ECC83, I've only heard good things about JJ valves so it's strange that the JJECC83S sounded muddy, maybe bajaman can suggest a good one to try.....

Time for another update:


Okay, my Marshall amp decided to blow it's HT fuse again today, so rather than get cranky at it I chilled out for a bit and made myself a cup of coffee, next I fitted a new fuse and tried powering up the amp again, result....the HT fuse blew the second I switched the amp off standby, I decided to see if I could figure out why the fuse was blowing so I got my multimeter and connected the black lead to the amp chassis, next I put the tip of the red lead on one of the connectors of the wires going to the standby switch and set it to off-standby, I set the multimeter on the 20M resistance range and watched the display, the resistance reading slowly dropped to about 300k ohms or so, I was wondering what would cause a reading that low, could it be that one of the 100uF/550V supply filter caps had gone lealy?, then I had a thought, could the output transformer have gone bad?, and I disconnected the wire going from the PCB to the output-transformer primary centre-tap while keeping the red probe tip where it was, the reading slowly increased to over 20M, next I connected the red probe tip to the connector of the output-transformer centre-tap wire and got a reading of 280k ohms, I was suspecting that the primary of the output-transformer had developed a partial-short to ground and decided to try removing the output valves one at a time to see if it was indeed the output-transformer or maybe something to do with the output valves,I removed the first output valve, the reading didn't change, I removed the second output valve.....suddenly the reading increased to over 20M ohms, Aha!, I thought...."a faulty output valve with a partial-short between pin 3 and pin 1 or 8?", when I replaced the valve back in it's socket the reading remained over 20M ohms, so, what had caused the 280k ohm reading?, I'm guessing that something had lodged itself underneath the valve and was causing a partial-short from pin 3 to ground, it had probably been there since the amps manufacture and I had inadvertently removed it when I removed the valve from it's socket, I replaced the valves I'd removed from their sockets, fitted a new HT fuse and put the amp-chassis back in the cabinet, tried the amp out and it was working again......now I'm wondering how long it'll be till the amp blows the fuse again.....touchwood......


So, I'm wondering what was causing the partial-short to ground, and, did I clear it just by removing the power valve and replacing it in it's socket?.......


I tested the valve for a partial-short between pins 1 and 8 and pin 3 with my multimeter set to the 20M ohm range, it looked okay.....

I have no idea as to which models this refers ,, But I did read way back on AGGH (I think)
that some of the later marshal's had inferior circuit board material that actually absorbed moisture.

And you do live in one of the most humid places in Aust. The symptoms you describe could well be this sorta issue.
Those boards slowly absorb moisture and after time you get a short between pins.
I do recall at least one Aussie Amp tech refusing to work on those amps as it's Marshalls problem but they refuse to recognize they screwed up or something along those lines. Apparently The big M won't cover the cost of repair.
Hope it's not that but thought I'd mention it.
Phil.

Or it could be an intermittent short in the second OP valve and pulling it out disturbed the short.
These are the original OP valves aren't they Simon?

deltafred wrote:Or it could be an intermittent short in the second OP valve and pulling it out disturbed the short.
These are the original OP valves aren't they Simon?

Yep, they are the original power output valves that were installed at the factory, I've been thinking about replacing all the octal sockets for the power valves with Ceramic types, the original are Beige coloured plastic ones, my thinking is that maybe the plastic in one of the octal sockets has become slightly conductive so replacing them with Ceramic ones will help things as the dielectric strength of Ceramic is very high, do you think it's worth it?.......

phatt wrote:I have no idea as to which models this refers ,, But I did read way back on AGGH (I think)
that some of the later marshal's had inferior circuit board material that actually absorbed moisture.

And you do live in one of the most humid places in Aust. The symptoms you describe could well be this sorta issue.
Those boards slowly absorb moisture and after time you get a short between pins.
I do recall at least one Aussie Amp tech refusing to work on those amps as it's Marshalls problem but they refuse to recognize they screwed up or something along those lines. Apparently The big M won't cover the cost of repair.
Hope it's not that but thought I'd mention it.
Phil.

Cheers for that mate, my Marshall is an MA100C and the power valve sockets are actually mounted on the chassis rather than a PCB, the preamp valves are PCB mounted though......

Simon
Don't replace the octal sockets - those Belton octal sockets are just fine. Deltafred is probably correct here - more likely to be an intermittant output tube short - usually the cause of random blown HT fuses. Without a tube tester though you are flying blind , however I would at the very least replace THAT tube with a new one and see how you go. If I had to recommend a type, I would suggest JJ, Winged C, and then Sovtek /EHX in order of preference. Phatt's comments are related to the infamous DHL and TSL 100 heads and combos - not one of Marshall's finest realisations. and YES - they (Marshall) are in complete denial - interestingly though tubesandmore.com stock a complete replacement board (minus tubes) for these beasts - it is the ONLY Marshall board assembly I have ever seen stocked

bajaman wrote:Simon
Don't replace the octal sockets - those Belton octal sockets are just fine. Deltafred is probably correct here - more likely to be an intermittant output tube short - usually the cause of random blown HT fuses. Without a tube tester though you are flying blind , however I would at the very least replace THAT tube with a new one and see how you go. If I had to recommend a type, I would suggest JJ, Winged C, and then Sovtek /EHX in order of preference. Phatt's comments are related to the infamous DHL and TSL 100 heads and combos - not one of Marshall's finest realisations. and YES - they (Marshall) are in complete denial - interestingly though tubesandmore.com stock a complete replacement board (minus tubes) for these beasts - it is the ONLY Marshall board assembly I have ever seen stocked

Okay then bajaman, I do happen to have a spare used Marshall EL34 valve packed away in a little box with some other valves, it was originally in a JCM800, i guess I could temporarily try using it as a replacement for that suspect EL34, and yes I totally agree with you, I seriously need to invest in some kind of valve tester, will have a look on eBay for one......





I might just go the whole hog and just replace all the power valves anyway, although the amp sounds okay it does seem a bit underpowered for a 100 Watt amp, anyway at least we know why the amp was blowing fuses, and at least we are making progress on it, I'm going to keep the amp since it does sound good when it's working, it seems a bit unusual to me for a brand new EL34 valve with an intermittent short being installed in a new Marshall amp at the factory, I always thought Marshall put all their valves through rigorous tests before they use them, maybe the quality control in the Vietnamese manufacturing isn't as good as Marshal UK's quality control, if so, Marshall UK should do something about it as I'm sure Jim Marshall wouldn't be too pleased to hear about the reliability issues of the MA series if he were still alive......


I dunno, maybe I'm being a bit naive here.....



What do you think about Groove Tubes EL34s, are they any good bajaman?......

just replace one tube at this time Simon

What do you think about Groove Tubes EL34s, are they any good bajaman?......

Groove Tubes is now owned by Fender - they buy tubes from many different manufacturers and then test and grade them according to the onset of 2nd harmonic distortion and output level.
For what it is worth I have still had bad tubes from groove Tubes in the past but have not had many dealings with them since Fender took them over.

Good advice from deltafred and bajaman - try replacing that suspect EL34 first. PM me if you don't have a spare handy and I'll try and get one to you quickly.

DrNomis wrote:I might just go the whole hog and just replace all the power valves anyway, although the amp sounds okay it does seem a bit underpowered for a 100 Watt amp, anyway at least we know why the amp was blowing fuses, and at least we are making progress on it, I'm going to keep the amp since it does sound good when it's working, it seems a bit unusual to me for a brand new EL34 valve with an intermittent short being installed in a new Marshall amp at the factory, I always thought Marshall put all their valves through rigorous tests before they use them, maybe the quality control in the Vietnamese manufacturing isn't as good as Marshal UK's quality control, if so, Marshall UK should do something about it as I'm sure Jim Marshall wouldn't be too pleased to hear about the reliability issues of the MA series if he were still alive......

Valves often get damaged when they (or the amp they're in) is shipped from one country to another. Having said that, properly packed valves should be able to withstand considerable shocks during shipping, and judging by the amount of supposedly brand new valves which have arrived over the last 10 years or so with faults that make them unusable, I'd say that manufacturing standards, quality control and packing methods are at an all time low. Compared to the 'Golden Age' of audio valves, say from the late 1950's to the mid 1980's.

OTOH, nobody was making guitar amps with the very high gain structures and inbuilt distortion capabilities that modern 'shredder' amps have, so maybe older valves had an easier job.

This is currently the cheapest seller of Shuguang EL34B's I've found in Australia:
https://www.ebay.com.au/itm/4-x-EL34B-S ... 3a8f2cba92

It's a bit odd that he quotes in US dollars, as he's in Adelaide; however he has a good track record on Ebay. I've bought capacitors and valve sockets from him previously, and I just ordered my first matched set of his EL34Bs.
I'll let you know if his service is good and the EL34B's arrive in good shape.

bajaman wrote:just replace one tube at this time Simon

What do you think about Groove Tubes EL34s, are they any good bajaman?......

Groove Tubes is now owned by Fender - they buy tubes from many different manufacturers and then test and grade them according to the onset of 2nd harmonic distortion and output level.
For what it is worth I have still had bad tubes from groove Tubes in the past but have not had many dealings with them since Fender took them over.

Cheers, I managed to find a spare used Marshall EL34 valve at home and I've used it to replace the suspect valve, will let you know how it goes.....

Simon. You could always build yourself a valve tester, something like this http://www.vintage-radio.net/forum/show ... hp?t=48853

It is something I think of every time I have a piece of valve gear on my bench. Once I have fixed it the desire to build one goes away.