Low voltage on finished Crack (repost)

[EricS]

I'm curious why a 5w sandcast resistor is open...  That's a pretty beefy resistor and I've never come across one that was DOA before usage.  Proceed carefully and check voltages and wiring as thoroughly as possible.  There may be a fault somewhere that caused that resistor to burn up.  If there is a problem, installing a new one will simply lead to it burning up as well. 

If you don't find an obvious wire fault, keep an eye (a temp probe?  a finger?) on that resistor for the first minute or two after you power up to look for "extra" heat.  Given that it's a B+ smoothing/dropping resistors, a temp of 30-50c might be normal.  30-40c means you can keep a finger on it indefinitely (watch out for the voltage - don't touch the lead!).  50c is a finger on it for <5s or so.  I'm gonna guess that you really shouldn't be seeing anything north of 70-80c.

[Deke609]

I thought the same thing, but the open resistor doesn't show signs of having been cooked. The writing on the body is still black, clear and even; and there is no discoloration of the leads from heat stress. Maybe a lead broke/disconnected inside the body - either at manufacture or subsequent twisting?

[Paul Birkeland]

Can you measure the DC resistance between pins 7 and 8 on the tube itself?

It is weird that the resistor is open, but I have seen that happen once in the last 25 years. 

[EricS]

Both of the above points (resistor doesn't appear burned and it seems rather rare to a new resistor that is DOA) make me think the problem lies elsewhere.  Are you getting good contact with your probes on the resistor leads?  Maybe some steel wool or gentle sand paper cleans something off of the leads that was causing a problem?

If this is not the case, your problem is most certainly elsewhere.  Search logically and methodically and start with most basic elements.  Work from the schematic and with your meter, cross off verified connections and note voltages on the diagram and move on.  You know generally where to look.  Start with the transformer, verify you're getting good AC voltage into it and good AC voltage out of it.  Check fuses, solder joints, voltages at each PSU cap, across the bleeder resistor, etc.

You'll find this - be logical, check every component and every wire, one at a time.     

[Deke609]

I'll probably try to look for it in a local hardware store. How much does it usually cost?

Mouser sells them for about a $1: https://www.mouser.com/ProductDetail/Yageo/SQP500JB-270R?qs=%2Fha2pyFaduiKZkvBfzT47gv2toBgzYfDhi5ak38cJcV7ykBbdTaI9Q%3D%3D

A North American hardware store selling construction tools and supplies is very unlikely to carry them. But a local electronics supply shop would most likely have something that would work - and maybe charge a bit more. Maybe 2$.  As PB wrote, anything 200-300 ohms and rated 5W will do.

cheers, Derek

[tsuid1]

Dang it, yeah I meant electronics store.

I measured the 7 and 8 pins on the tube and got a resistance around 1 ohms.

My dad was testing the voltages and resistance using the schematic, and the only issue he found so far was that dead 270ohm resistor. Right now, I'm going to look for any weak soldering joints, weak resistor probe connections, voltages, sawdust etc.  Is there anything else I should look for in the mean time? Do the probes have to be completely through the hole on the terminals if it's connected by solder?

[Paul Birkeland]

You have to get the 6080 glowing before you do anything else.  If pin 7 to 8 on the tube measures 1 ohm, the tube should glow.  Perhaps the green wires running to the octal socket aren't well connected?

[tsuid1]

Hi guys, first off sorry for the radio silence, I had relatives over these past few days, so I didn't have time to work on the amp. Customer service got back to me and said the resistor is headed my way.

I've been inspecting the amp, but so far I don't see any issues with sawdust. My dad inspected the solder joints and everything seems fine.

Here are some photos of the green wires

[Paul Birkeland]

Neither of those green wires is well soldered to the power transformer.  You need to wrap the free end of the wire up and over the transformer terminal, then solder.  The solder should flow into the area where the wire is wrapped around the terminal.

Just poking a wire straight through and hoping the solder will make a good connection is not adequate.

[EricS]

Lots of visual examples of good and bad solder joints:

https://www.google.com/search?q=proper+solder+joint&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiGqZONtqnnAhXjmXIEHbYCD2EQ_AUoAXoECA4QAw&biw=1312&bih=693

[tsuid1]

Being able to see a proper solder joint helps alot. I'm going to study up on this before working on it. Thanks!

As for the wires, yeah it looks like I didn't properly wrap and solder the wire around properly. I cut what I thought to be excess wire after I bended and soldered it. I'll probably strip a bit of the coat off and wrap the wire around

[tsuid1]

Hi, sorry for the late reply. I haven't had time to work on this until recently. I was able to get the 6080 to glow after installing the resistor. All the voltages are in order. However, I ran into a couple of issues

1. There is a channel imbalance with a bias towards the left side. I checked the inputs and they seemed to be wired correctly. Wetted and added a bit of more solder to the red rca but nothing really changed. There also is a very very low hum in the right side, but I have to concentrate to notice it.

2. I had some issues with the audio. When I listened, the bass was boomy, midrange was dry, treble was recessed, and there was little to no soundstage and depth. I wetted and added more solder to any cold joints I could spot and now it's pretty neutral; midbass has drastically reduced to being linear, midrange is a bit sweeter, and treble is more airy. It sounds identical to the Atom. From what I read, the stock crack is supposedly a warm sounding amp, but I'm not too sure if what I have is right or wrong.

One thing to note is that the black wire connecting the headphone output and terminal 12 is soldered on 12u as opposed to 12L. The new resistor is soldered on terminal 13 and 15 standing up. Would that be part of the issue?

[Deke609]

Re audio/listening issues:

(1) What headphones are you using?

(2) Give the amp time to break/burn-in before doing any critical listening tests. The caps and tubes take time to settle into what will become their normal operating characteristics. To get there, you need to put signal (music) through the amp (with headphones connected or with other suitable load) for at least 50-100 hrs.  The sound can change quite a bit during the break/burn-in period. In my limited experience, the bass is the last thing to finally settle. My approach is to run an amp that needs break/burn-in in 12-20 hr sessions - letting the amp cool to room temp between sessions. 

Re installation issues: Installing a component on the upper vs./ lower lug, or vice versa, shouldn't make any noticeable sonic difference. Same goes for installing the 270R resistor standing up. But I suspect having the resistor flat against the chassis and away from the caps is much better for dissipating heat. Those resistors get hot and caps don't like heat.  PB will be able to tell you whether this is a problem in your case.

cheers, Derek

[tsuid1]

Thanks. This is good advice. I'm running them with my HD 600. As far as burn in, I've ran it for about alittle more than 20 hours approximately. I'll let it burn in more

[Paul Birkeland]

Your description of what the amp sounds like is how I would describe the sound of cold solder joints.

Channel imbalance is somewhat covered in the FAQ sticky on this board, but also be aware that cold solder joints can definitely cause this too.