Hiwatt Gurus: Help your friend Bob!
Moderator: Mods
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Hiwatt Gurus: Help your friend Bob!
howdy bros. hiwatt bob here. so the other night i was showing off my DR504 to some dinner guests--i was sort of in a rush so i didn't let the tubes warm up as much as usual. i dimed it just to scare them with volume--and it fizzled out quickly, almost like the sound you get when you power down and keep playing.
i figured i'd blown an output tube--but when i sat down tonight to try to figure it out, i tried a couple different sets of output tubes and no sound. i subbed in different preamp tubes in each position and still no sound.
the pilot light is on, all the tubes glow. i have a bias rite--and it showed the plate voltage to be around 530V on both tubes). the cathode current (mA) reading was 0 however.
took a peak inside and didn't notice any burnt parts/scorched earth. both fuses looked fine. at the time it happened i didn't notice any burnt smell, etc.
any ideas?
hopefully it's not something serious like a dead partridge.
any help is much obliged.
i figured i'd blown an output tube--but when i sat down tonight to try to figure it out, i tried a couple different sets of output tubes and no sound. i subbed in different preamp tubes in each position and still no sound.
the pilot light is on, all the tubes glow. i have a bias rite--and it showed the plate voltage to be around 530V on both tubes). the cathode current (mA) reading was 0 however.
took a peak inside and didn't notice any burnt parts/scorched earth. both fuses looked fine. at the time it happened i didn't notice any burnt smell, etc.
any ideas?
hopefully it's not something serious like a dead partridge.
any help is much obliged.
Re: Hiwatt Gurus: Help your friend Bob!
Since you've already tried different sets of output tubes----- and all have normal plate voltage but no current draw----#1) see if the Screen Grid resistors have failed--if screen grid resistors measure ok and screen grid voltage is good (close to plate voltage) on the tube socket pins (pin 4)--- then, #2) suspect failed OT
Re: Hiwatt Gurus: Help your friend Bob!
Dumb question -- you did check the HT fuse, right?
--mark
--mark
- OldSchoolDave
- Posts: 2060
- Joined: Wed Nov 14, 2007 9:24 pm
- Location: HP, NC USA
- Contact:
Re: Hiwatt Gurus: Help your friend Bob!
...as in, with a continuity tester/multimeter - not simply via visual inspection?mhuss wrote:Dumb question -- you did check the HT fuse, right?
I'd also pull the impedance selector and check for oxidation. Sometimes, just re-seating those can clear things up.
Dave
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
i have a multimeter--what do i set it to in order to test the fuse? impedence?
i'll try the impedence selector plug.
how would i go about testing the screen grid resistors? i'd feel comfortable enough safety-wise to do it, just don't know which points to put the multimeter to, etc.
thanks boys!
i'll try the impedence selector plug.
how would i go about testing the screen grid resistors? i'd feel comfortable enough safety-wise to do it, just don't know which points to put the multimeter to, etc.
thanks boys!
- mikhailwatt
- Posts: 858
- Joined: Thu Nov 15, 2007 2:46 am
- Location: Austin TX
Re: Hiwatt Gurus: Help your friend Bob!
Check the fuse for continuity/resistance (ohms) - should read zero ohms if it's good (continuity), megohms if it's blown (open circuit).Hiwatt Bob wrote:i have a multimeter--what do i set it to in order to test the fuse? impedence?
i'll try the impedence selector plug.
how would i go about testing the screen grid resistors? i'd feel comfortable enough safety-wise to do it, just don't know which points to put the multimeter to, etc.
thanks boys!
Check the resistance (ohms) across the screen grid resistors. If they're original equipment they're probably 100 ohm. If they've been replaced they might be 1K ohms. If you get super-high readings, you've got an open (blown) resistor.
You can almost feel the current flowing
You can almost see the circuits blowing
You can almost see the circuits blowing
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
hey mikhail--
anyway you could point out which points i need to check--are they the big white ones on the output tube sockets? also, if i'm just measuring resistance, i don't need to have the amp fired up--correct?
anyway you could point out which points i need to check--are they the big white ones on the output tube sockets? also, if i'm just measuring resistance, i don't need to have the amp fired up--correct?
- Dr.HI-TONE
- Site Admin
- Posts: 2675
- Joined: Wed Nov 14, 2007 8:51 pm
- Location: HIWATT Valley
Re: Hiwatt Gurus: Help your friend Bob!
Hi Bob,
correct, the big white ones and the amp does not need to be powered up for this.
I hope it is a simple fix!
correct, the big white ones and the amp does not need to be powered up for this.
I hope it is a simple fix!
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
thanks Doc Callowatt--
i'll try this stuff tonight and let you guys know what i find.
i'll try this stuff tonight and let you guys know what i find.
- OldSchoolDave
- Posts: 2060
- Joined: Wed Nov 14, 2007 9:24 pm
- Location: HP, NC USA
- Contact:
Re: Hiwatt Gurus: Help your friend Bob!
I'll keep my eyes open for a purple flash on the southeast horizon .Hiwatt Bob wrote: i'll try this stuff tonight and let you guys know what i find.
Dave
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
hopefully there will be no purple flash--just a sonic boom.
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
ok.
tried the speaker ohm selector plug--that doesn't seem to be it.
measured the impedence on both fuses. both read very low (or high i guess)--like maybe 5 ohms (i think). they measured the same as new ones i have.
measured the screen grid (they are 1K's) and they both measured like 930-ish.
so you guys think i've got big problems?? is there anything else i can do/try? anyway to find out if it's a blown output transformer (sure hope it isn't this).
tried the speaker ohm selector plug--that doesn't seem to be it.
measured the impedence on both fuses. both read very low (or high i guess)--like maybe 5 ohms (i think). they measured the same as new ones i have.
measured the screen grid (they are 1K's) and they both measured like 930-ish.
so you guys think i've got big problems?? is there anything else i can do/try? anyway to find out if it's a blown output transformer (sure hope it isn't this).
Re: Hiwatt Gurus: Help your friend Bob!
It seems that you eliminated the most common failure points.
I once had an output tube blow on one of my Hiwatts and it also took out a screen resistor, at least one electrolytic capacitor (I replaced them all), and a fuse. I suppose there's a chance you blew an electrolytic cap?
I thought that an output transformer would smell after it fails, but maybe not after a thermal shock incident.
It is best to play at low volume after start-up and roll up the volume to prevent thermal shock to the speakers and the amp's components.
We'll all keep our fingers crossed with hopes of the OT being well.
I once had an output tube blow on one of my Hiwatts and it also took out a screen resistor, at least one electrolytic capacitor (I replaced them all), and a fuse. I suppose there's a chance you blew an electrolytic cap?
I thought that an output transformer would smell after it fails, but maybe not after a thermal shock incident.
It is best to play at low volume after start-up and roll up the volume to prevent thermal shock to the speakers and the amp's components.
We'll all keep our fingers crossed with hopes of the OT being well.
Re: Hiwatt Gurus: Help your friend Bob!
Measure some voltages (carefully!) with the amp on, not standby. Connect the black lead to the chassis, and use the red lead to measure (use the 600v DC setting or similar).
1) Voltage at the pins of the two 200uF caps nearest the fuses.
2) Voltage at the each of the pins of the output tube sockets (be very careful here, a slip of the probe and it's blue flash time!*)
--mark
* You need DR201 or DR405 voltages to get the true purple flash.
1) Voltage at the pins of the two 200uF caps nearest the fuses.
2) Voltage at the each of the pins of the output tube sockets (be very careful here, a slip of the probe and it's blue flash time!*)
--mark
* You need DR201 or DR405 voltages to get the true purple flash.
-
- Posts: 148
- Joined: Sat Dec 01, 2007 10:48 pm
- Location: Minnesota
Re: Hiwatt Gurus: Help your friend Bob!
ok.
i got 30V on each of the electrolytics.
i got the following (same measurements for each output tube, see pic) measurements on the pins
(1) 60V
(2) -40V
(3) Overload -- i was able to at least hear some audible crackling when i touched to these pins.
every other pin read 0.
i got 30V on each of the electrolytics.
i got the following (same measurements for each output tube, see pic) measurements on the pins
(1) 60V
(2) -40V
(3) Overload -- i was able to at least hear some audible crackling when i touched to these pins.
every other pin read 0.