Only a blown fuse? Anything else I should know?

Greetings to the group.

Well, how long have I had my ST70 now, 3 years? No problems at all. But tonight I had an impulse to play an old Led Zeppelin record from my youth. 3 bars or so in I decide it's better left to the memory banks. Couldn't stand to listen to it.

Down went the volume, off came the needle, but then a crackle, and the ST70 goes cold. I thought it was the rectifier, so replaced it with a spare Ruby, and nothing. The fuse. Must be the fuse.

Sure enough, the glass is scorched, and the fine coil of wire that wraps around . . . something. A thick piece wire, it looks like. Well it's broken.

So, I take it the fuse is burned out then.

I have no idea why this happened. Lights didn't flicker like there was a power surge or anything. Shall I just replace it and see what happens?

Any advice is appreciated.

Thank you.

Hey Tube Nube,

That's not good to hear....

I would take the bottom cover off and visually check all the components and wiring for any signs of overheating or shorting (scorch marks on a resistor or cap) that might account for the extra current draw to blow the fuse.
If all looks alright then replace the fuse and recheck the tube bias voltage and hope it's all good.

No doubt Bob will chime in with a comprehensive check list.

What Led Zeppelin album were you playing?
Zeppelin were my favorite band when I was growing up ... Physical Graffiti was the 2nd record I ever bought back when I was 14

Thanks guys for your immediate feedback. What a great group this is! I post a problem before bed time, and two helpful messages are here for me as soon as I awaken.

Alan, it was the song Dyer Maker -- I forget which album. Old Robert Plant coulda been singing to my fuse there: "Oh, uh-oh ah oh-oh," {wait for it guys. . . } "you don't have to blow-oh".

Sorry, I couldn't resist.

Bob, thanks for recommending the rectifier along with the fuse. I was going to just change the fuse and try again. I have two spare rectifiers, the original Sov Tek and another Ruby.

I'll get a hand full of fuses and report back this afternoon.

Ah ... D'yer Maker ... that's one of my favorite Zeppelin tracks. I don't think it sounds that bad ... LOL
It's off the album Houses Of The Holy

And another bit of trivia ... my first ever record was Bachman Turner Overdrive's Not Fragile ... I do believe those guys were from your neck of the woods

Hi Alan, you are right. Funny, they are from my neck of the woods, and I'm originally from your neck of the woods (born in Sydney).

I had a client, once upon a time, who was a friend of Randy Bachman. He had some good stories.

Thanks Bob, I did get GDL3-AT fuses that claim to be 3A "time delay fuses".

Think I'll save the fun for after I mow the lawn. Give me something to look forward to. To work for!

So did your parents migrate over to Canada or did you move over yourself later in life?

No doubt your client would have had some "interesting" stories about Randy Bachman

It's raing here this morning so no chance of mowing any grass ... damn ... might have to get out another CD and play it through some warm valve goodness

Hi Alan,

Yes, my parents moved us to Canada when I was 5. Some story about more opportunity in this country!

Ok. So I replaced the fuse and rectifier. It came on, and about 30 seconds in, there was crackling and buzzing from the left channel, and a bit of a light show coming from the right rear KT 88.

I presume this means that tube is probably done? I do have a pair of spares from the same brand . . . Do I go ahead and put in one or both right side tubes?

Opinions? Ideas?

Gentlemen, place your bets!

As to the lawn . . . well, I shouldn't have let the grass grow to 8". This is gonna be a two day job, at least! Al, I say go for it.

Ok, I risked it. I replaced the two right side KT 88 tubes with the spare pair, switched on, sat there waiting for trouble and nothing. After a couple minutes, I biased all tubes to 490 . . . millivolts I guess it is. Plus or minus. Amp's been warming up a few more minutes, and no snap crackle pop, so time for a listen to some actual music I say!

Mowing long grass is a pain in the arse!

Not good with that output tube flashing over like that ...
I had one of my output tubes flashover as well not long after firing up my ST-120 for the first time as I cranked the volume up a bit.
But 140 hrs later that tube is still running fine.

Since you're replaced the rectifier tube I would re bias all the output tubes as the new rectifier might be out putting more than what the old one did and perhaps that caused the flashover.

Follow Bob's bias setting process from the original start up procedure ... turn all the bias pots down to minimum before powering up the amp and start from there.

I'm not sure if you would have to replace the pair of tubes because individual biasing removes the need of a "matched" pair.
Maybe sonically it might be better to repace the tubes in pairs ...
I'm sure others with more valve experience will let us know


Ah ... you beat me to it ... LOL

All sounding good now Brenton?

I've been listening to Joan Armatrading's Me, Myself I CD this morning ...
In fact I had to listen to it twice I enjoyed it so much ...

The combination of Bob's ST-120 and Roy's SP-14 is amazing ...
The only downside now is ... I need better speakers ...

Hi Alan,

I may just have to check out Joan Armatrading. I'm familiar with the name, but can't think of any of her tunes.

You're right about the great sound. I've got the SP14, and it's a big improvement over the SP8, which I really loved! Still love. Just not as much.

;-)

As to speakers, I wonder would you ever consider building them yourself? I was was in your dilemma, worried that worthy speakers would cost me a bundle when I tumbled to the idea of DIY, and I had no wood working skills, nor had I used anything bigger than a hand drill in 35 years.

I've saved a bundle of money, and only spent . . . a smaller bundle.

This ought to warm the collective hearts of you, Bob and Roy, as it does me.

A friend of mine has a life long interest in hi fi. More at the speaker end of things -- a physicist by training, he designs and builds subwoofers and has written a number of articles published in audio magazines over the years on such things as subwoofers, room acoustics, etc.

Well, he was over for a listen last week, and while he noted the lack of low end (below 100hz) from my speakers -- a common problem -- he otherwise was just thrilled with the sound of the stereo. He said it was the best he's ever heard in his life.

I've always enjoyed wowing my friends, but I was quite nervous to have this guy hear my gear. What a thrill, I must say, to hear his enthusiastic praise.

Tube Nube wrote:Hi Alan,

I may just have to check out Joan Armatrading. I'm familiar with the name, but can't think of any of her tunes.

You're right about the great sound. I've got the SP14, and it's a big improvement over the SP8, which I really loved! Still love. Just not as much.

;-)

As to speakers, I wonder would you ever consider building them yourself? I was was in your dilemma, worried that worthy speakers would cost me a bundle when I tumbled to the idea of DIY, and I had no wood working skills, nor had I used anything bigger than a hand drill in 35 years.

I've saved a bundle of money, and only spent . . . a smaller bundle.

Hey Brenton,

Yes you should look at buying Joan Armatrading's "Me, Myself, I"
Once you start going through it you will recognise a few songs.
And the best part is that it's really well recorded with lots of impact and dynamics and subtle nuances ...
I have it in both vinyl and CD versions ... and the vinyl version just has that presence and warmth that the CD version can't match


As far as speakers go ... hell yeah I will be building my own!!!!!!!

These are the speakers I'm going to build ... http://www.troelsgravesen.dk/JA8008_DTQWT.htm
I have a friend of mine who is a cabinet maker and I asked him today if he would build the boxes for me as they are a bit complicated ... and I want them to look like a nice piece of furniture ... and with wood working I don't have the tools or the skill to get the quality I want.

I'm hoping to order the components some time this week ...

Tube Nube wrote:This ought to warm the collective hearts of you, Bob and Roy, as it does me.

A friend of mine has a life long interest in hi fi. More at the speaker end of things -- a physicist by training, he designs and builds subwoofers and has written a number of articles published in audio magazines over the years on such things as subwoofers, room acoustics, etc.

Well, he was over for a listen last week, and while he noted the lack of low end (below 100hz) from my speakers -- a common problem -- he otherwise was just thrilled with the sound of the stereo. He said it was the best he's ever heard in his life.

I've always enjoyed wowing my friends, but I was quite nervous to have this guy hear my gear. What a thrill, I must say, to hear his enthusiastic praise.

How cool is that ... I bet you had a smile from ear to ear

Thanks to Bob and Roy I now have the high end audio system that I have always dreamed of but could never afford

Alan,

Those are stunning looking speaker. The cabinet construction doesn't look like it will be any problem for your friend to do a fantastic job with his cabinetry skills.

I was perusing the site you linked to, but dont' have time to really explore it now, but I will do so later on, as that looks to be a very interesting speaker indeed.

Regarding my friend's visit, yes. It was such a treat to have a guy so knowledgeable, listening with his discerning ear, telling me with such delight about what he's noticing in the sounds. His detailed comments about the imaging and sound stage, his ability to follow multiple things at once that different musicians were doing etc, compared to when he listens to the same recording (Graceland) at home.

I encouraged him to let me have the bad and the good, and I think he was genuine. It's always nice to have someone say "oh, that sounds good", but to hear the praise from a guy who's so knowledgeable -- It did make me grin from ear to ear.

Not that I should be surprised. Bob's experiences that he notes above are as amusing as they are satisfying, and he forewarned me a few years ago that these amps really punch above their financial weight class -- especially when compared against specialty boutique name brands.

Encouraged by recent experiences, I'm really eager now to get the friend of a friend over here for a listen. He has a reputation as something of an audio phile. If not mistaken, Krell his brand. Even if his own stuff is stellar, I have no fear of being shamed.

It's fun to share!

Brenton,

Those speakers have been designed for high eficiancy to be suitable for valve amps.
The designer Troels Gravesen is a die hard valve afficionado himself and these are his flagship speakers.

The feedback on these speakers are that they are something special indeed.
We have a HiFi forum here in AUS called StereoNET and on the weekend I stumbled apon a member that had built these speakers last year.
He's had a couple of sessions where other forum members went to his place to audition his speakers and all came away very impressed ... and these guy's are like your friend ... hard core audiophiles who aren't easily impressed ... but they were in this case.

Seems like we both have the same speaker issues ... a lack of low end bass.

Do you have any pictures of the speakers you use?

I have a feeling your audiophile friend will be suitably impressed with your system ...

Hi Alan,

Having a hard time here figuring how to post a photo. Maybe I'll pm it to you.