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Post subject: Found this while bias checking new tubes 98 Hot rod Deluxe
Posted: Wed Mar 11, 2015 1:45 pm
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17 year old filter caps ((( Yikes ))) !
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close up in case you missed it
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I just happened to get down low and look up and well...... a set of three 22uf 500 Volt and a 47uf 500 volt F&T are on the way.

glad I caught it before i smoked it ! by the way the test point 1ohm resister was closer to 1.3ohms
so I used my own tube fitted test point.

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 11, 2015 2:42 pm
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Good catch. I don't like the way these are on the circuit board. Potential for damage, if they leak out.

1.3 ohms is 30% off! That is crazy. Is that a 5% tolerance resistor? Did you lift a leg prior to measuring the resistance? For these circuits with 1-ohm resistors to measure voltage drop, I like the 1 or 2% tolerance types.


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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 11, 2015 2:56 pm
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Good catch! Better to change before sound degradation is apparent.

Same with my '98 HRDlx. I caught the first leaking IC cap after around 13 years or so, and changed all to F&T, adding an extra 47 µF in the first stage to tighten the bass a little. My TP resistor is also about 1.3 ohms, and if you use the actual value for calculating the current, you can get an accurate setting. I do prefer bias probes though, allowing check for matched sets of output tubes.

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 11, 2015 3:40 pm
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I'm ready for the whoop'n I'll get however, I'm seriously thinking about clipping the old caps close and making a connecting loop for the new ones, tell me why I shouldn't
Removing that board is the last thing I wanna do !
I did finally get myself a good Weller adjustable wattage soldering station a while ago, man that helps !

so is that type of joint a completely bad thing ? I've opened up several cap housings to find a twisted and soldered connection.

No beemer I didn't pull a leg on that resister, its a metal oxide on the bottom of the board so......... 8)

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 11, 2015 8:28 pm
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When measuring very low ohms, first measure your test lead resistance.
Just short the probes and see if it goes to zero. Then subtract that from your test results.
My Fluke"s leads are .3 ohms. My cheap leads are .6 ohms
It shouldn"t affect voltage readings.


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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 11, 2015 9:08 pm
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Changing caps like that on a pcb is not the same situation as poin to point. P-P is strong.
There is not as much mechanicel strength with a pcb, so the solder can crack more easily.
Cut the cap loose and use 2 pairs of needle nose pliers. One to hold the lead securely at the pcb and the other to bend the loop. Glue the new ones down with silicone

But if the amp hasn"t been serviced before, it migh be worth dropping the board down to do it. A 98 is probably due for other minor maintenance.
Check for radial cracks in the soldering on the jacks, ,the controls, the 5 watt resistors, 1N5353 zener diodes and tube sockets.
Be sure to replace the zip ties.
Clean the NC switch contacts on the external speaker jack with solvent on a strip of card stock.


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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 2:06 am
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Yeah, I have to agree with TimsAudio. As tempting as it is to take the shortcut, this opportunity to pull the board and check the solder joints could prevent some heartache later. Personally, I couldn't stand the thought of a "half-assed" job of replacing caps without pulling the board. It is worth the effort, and it looks so much more professional, when done the right way.

Just use reasonable care, try to let the ribbon cables flex in the middle and not at either end where they meet the boards. The board isn't quite as delicate as some people let on. I have pulled mine numerous times, changing caps, trying CC resistors and then pulling them back out (CC suck!), putting in new jacks (two different kinds). I have never broken anything. :)

BTW, I would go ahead and dress the leads while you are at it. Every little bit helps.
Image

AAMOF, why not change the jacks while you are in there?
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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 2:38 am
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blues bondsman wrote:
I'm ready for the whoop'n I'll get however, I'm seriously thinking about clipping the old caps close and making a connecting loop for the new ones, tell me why I shouldn't
Do not do that you may do a bad connection under the PCB or / and short with melt solder

Removing that board is the last thing I wanna do !
No choice if you want a reliable amp

I did finally get myself a good Weller adjustable wattage soldering station a while ago, man that helps !

so is that type of joint a completely bad thing ? I've opened up several cap housings to find a twisted and soldered connection.

No beemer I didn't pull a leg on that resister, its a metal oxide on the bottom of the board so......... 8)



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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 7:43 am
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Well shoot !
about 45 minutes to pull the board and the caps, no biggie !
I've pulled a few Blues jrs boards, thought this was gonna be a tougher one, turns out it was very simple :mrgreen:
Image
Image
Image
waiting on parts now, hopefully by the weekend !

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 10:18 am
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went by my local electronics parts house and they had the zener diodes 16v 5W
however all they had were 10W 470 ohm wire wound resistors (see picture)
might be a bit of a space issue ?
Image

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 12:14 pm
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You can stack two 1000 ohm 5 watt resistors paralleled in the same footpriny to reduce board overheating.
Use silicon to fasten them to the board and each other. Then make a bead on top between the two pairs for vibration control.

The new zeners have nice long leads. Form them into a 1/4" inside loop so the leads are properly spaced for the holes. then lay the loops on a flat surface and fill them with solder to create a heat radiating fin for extra cooling topside.

I also scrape the green solder mask away from the resistor and zener traces @ 1/2" and tin them for additional bottom side cooling. I wish Fender would make this one simple mod to improve reliability. If they would also widen the traces here, it would eliminate this "Achilles Heel" of a very fine amp.


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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Thu Mar 12, 2015 4:17 pm
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sounds good Timsaudio

I made the 10 watt resistors fit and can't imagine a heat problem again.
The diodes are double the distance from the board and solid so.......
hopefully the dude I bought the caps from over east of here actually has them moving my way :mrgreen:
stink'n post office has been horrible with tracking lately !
I have had excellent results with F& T caps over the last few years, i'm bett'n this amp will sound WAY better after this tune up.
it lasted 17 years with what looks like only minor surgeries (input jacks had been changed).

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 18, 2015 11:09 am
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Well I didn't get a picture
New zeener diodes, new power supply resistors and all new F&T filter caps
She is all better now ! 8)

I did use those 10 watt wire wound and gave them legs with knees to get them off the board, those dudes should last a lifetime !

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 18, 2015 5:52 pm
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A job well done!

How does it sound?

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Post subject: Re: Found this while bias checking new tubes 98 Hot rod Delu
Posted: Wed Mar 18, 2015 6:38 pm
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5751 in v-1, a good 12AX7 in v-2 and a 12AT7 in v-3 makes the HRDX stand tall !
Sounds Great

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2017 50's Baja Telecaster BSB

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VHT Special 6 Ultra combo

Visual Sound Route 66
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