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dalemurray wrote:Nice while it lasted. Just blew the slow blow fuse after about 1 hour of low volume listening.
To the manual. Hope I can figure out what I did wrong. I also have to figure out where I can get more of these fuses.
dalemurray wrote:Nice while it lasted. Just blew the slow blow fuse after about 1 hour of low volume listening.
To the manual. Hope I can figure out what I did wrong. I also have to figure out where I can get more of these fuses.
peterh wrote:
How did you blew it ? What was the sequence of events ?
A power off/on sequence could easily result in a broken fuse.
dalemurray wrote:peterh wrote:
How did you blew it ? What was the sequence of events ?
A power off/on sequence could easily result in a broken fuse.
Amp had been on for about an hour and playing at very low volume (low enough not to wake my wife at the end of the hall). The tone of the music changed and faded out over the course of a couple seconds.
I passed all the start up tests without issue.
Peter W. wrote:dalemurray wrote:Nice while it lasted. Just blew the slow blow fuse after about 1 hour of low volume listening.
To the manual. Hope I can figure out what I did wrong. I also have to figure out where I can get more of these fuses.
First some math:
You will need to calculate (roughly) how much current your amp *should* be using.
KT88 x 4 makes:
4 x 1.6A x 6.3 V = 41 watts (all results-figures rounded up) on the filaments
(35 + 6) x 4 = 164 watts dissipated in music and/or heat
Each of your small-signal tubes dissipates about 2 watts as above.
5AR4s dissipate about 200 watts at peak.
Makes a total of 251 watts or so. BUT, you ask, what about the 5AR4? - the current it dissipates is what is being used down-line.
Pull all the tubes, plug it in, turn it on. Read the current. That will give you transformer losses - but, generally, I look at about 10 watts per-each to be conservative. Mostly, and with Bob's transformers, losses will be under 10%, but let's use 30 watts. And as we are rounding, make the total to be consumed at 281 watts. Make your wallplate voltage at 120 VAC. Makes for 2.4 A THAT!! is the amount of actual current required by your amp at peak. I believe that the nameplate on these amps is 275 watts. So, close-enough.
Peter W. wrote:
Do you have the means to test tubes?
dalemurray wrote:Peter W. wrote:
Do you have the means to test tubes?
I do not. Sadly, I gave a tube tester away to a friend a few months ago because "I would never need it". It was going into the garbage from an estate so I grabbed it for him. I could always borrow it for a bit, I am sure.
Peter W. wrote:
If you are anywhere near 19027 or 17859, I have a big Hickok. If the decay took more than a few seconds - that is, happened before the fuse blew, rather than as a result - it could be bad tube(s).
dalemurray wrote:peterh wrote:
How did you blew it ? What was the sequence of events ?
A power off/on sequence could easily result in a broken fuse.
Amp had been on for about an hour and playing at very low volume (low enough not to wake my wife at the end of the hall). The tone of the music changed and faded out over the course of a couple seconds.
I passed all the start up tests without issue.
corndog71 wrote:Where did you get your tubes from? I've had several rectifiers break right out of the box back when I was buying the cheapest tubes I could find. The yellow sheet mod can help but your 5AR4 may be shot.
I highly recommend Jim McShane for quality, tested tubes at a fair price.
Peter W. wrote:Yikes!!
First, check all the bias resistors and make sure they are intact and connected properly. With a dental pick, check _ALL_ the connections to the tube sockets, boards, terminal strips and so forth. ALL of them. You are looking for a cold/broken/incomplete solder. Be systematic, and work in really good light.
Obtain a new 5AR4. The post-blight examples seem to be about as sensitive as our president's ego to any sort of rough treatment.
Peter W. wrote:
With inputs shorted and speakers connected:
Run the bias pots half-way up if below half now. This will be your starting point moving forward, but assure there is *some* C- on the output tubes.
(A+ = Filament voltages; B+ = operating/signal voltage; C- = Bias Voltage)
Peter W. wrote:
Keep the bias voltage at/about your target voltage. After +/- 15 minutes, it should be sufficiently stable to set permanently - but check again in one hour. Note that the bias voltage is not dependent on the 5AR4, and should be present very nearly at turn-on. In point-of-fact, you can set all this without the 5AR4 in anticipation of its arrival. It will change as the transformer is loaded with B+, but a good start.
sKiZo wrote:Double check the multi can cap. If you were able to power up and listen for a while, the connections should be correct, but I'd resolder them anyway, and make sure the can is tight and solid to the chassis.
sKiZo wrote:Oh. As mentioned, a slow start board can work wonders if you go thru a lot of rectifiers, as it's the initial surge on startup that really hits em hard, especially if your wall voltage tends to run high. I strongly recommend going with a thermistor in line with the main hot - that ramps up over a few seconds and never goes completely open, so you get the slower start AND it should drop line voltage 1-2vac. Another option is the WS68 copper top solid state rectifier. That also has the slow start built in. And yes, I know Weber now recommends the WS1 for straight audio amps, but I take that with a pound of salt. I've run a WS68 here with nary a problem, and other folk have used them for years. I've since gone with a Mullard GZ37 big bottle, and that seems to be pretty much bulletproof, but those are getting hard to find and tend to cost some big bucks anymore.
** I've also had no issues using a CL90 thermistor. And yes, the amp DOES draw more than what that unit is rated for, but that's only under full load, and that's only intermittent at most. Never had any problems here, and I've run them on 10 amp loads. The recommended thermistor is a CL80, but that tends to run a lot hotter. In either case, make sure to allow max clearance to any other components as both need room to breathe.