Gretsch Fury 6169 on the bench

[TubeGeek]

This one is a fair bit of work to sort out.  It's a wonky stereo design.

One power supply stage with two output stages.

[sluckey]

Don't you just love looking at that artwork? You've come a long way since that Vibro Champ.   

[TubeGeek]

Don't you just love looking at that artwork? You've come a long way since that Vibro Champ.   

You still remember that?!!!  That was almost 20 years or so ago… I was a sponge, soaking up all the info I could absorb.


I learned a valuable lesson on that project which was one of my first builds.  Second or third I believe.  I went from my first build being an AB763 twin reverb to a princeton and vibro-champ

[PRR]

Not actually stereo. Two inputs, two outputs, but it all comes together at the input to the power stage.

At that, it is still a LOT less of a mess than most Fisher stereo tube hi-fi amps.

[sluckey]

You still remember that?!!!

Some things are very memorable. The important thing is that you still remember.   

[WimWalther]

Wow, that Mallory cap really let go! What a mess.

[TubeGeek]

Wow, that Mallory cap really let go! What a mess.

Yeah good eye.


It was not stock.  Previously installed I'm assuming to reduce hum.  It was loose in the chassis

[WimWalther]

Wow, that Mallory cap really let go! What a mess.

Yeah good eye.


It was not stock.  Previously installed I'm assuming to reduce hum.  It was loose in the chassis

Yeah, assuming that 450V is sufficient, I guess it wasn't up to the ripple current that it had to deal with, right off of the rectifier. Looks to have been a used part at that, with the riveted clamp.

[TubeGeek]

Update:


I finally got around to completing the cap job.  I left the original cap cans in place and opted to install discrete caps inside the chassis.  It was quite a bit of work but I got it done and chased out 4 or 5 gremlins.  Now it's sounding pretty good. A world of difference from before the cap job.  Big improvement.


Time to wrap my brain around this design. 


Am I wrong to assume I can send the output to two separate speakers simultaneously?


I know it's not true stereo but why have the TRS output jack?  I thought one pair of 6L6's go to one speaker and the other pair of 6L6's would connect to another speaker?


What I am getting is barely anything substantial on the second speaker cabinet I have connected.  It's there but very weak and it's overwhelmed by the main speaker output to the first speaker.

[shooter]

got this from Doug's library, seems to show 2 speakers, one driven by each OT

[sluckey]

I know it's not true stereo but why have the TRS output jack?

Both speakers are in the same cab. The engineers chose to use a TRS jack for simplicity. Makes sense to me. They could have chosen to use two mono jacks but then you would need two speaker cables to connect the single speaker cab.

I thought one pair of 6L6's go to one speaker and the other pair of 6L6's would connect to another speaker?

That's correct. But both speakers are in a single cab. Do you have the Fury cab and original TRS speaker cable?

What I am getting is barely anything substantial on the second speaker cabinet I have connected.  It's there but very weak and it's overwhelmed by the main speaker output to the first speaker.

Are you using a TRS jack to connect the two speakers to the amp? Is is wired properly? You have two identical P/P 6L6 power amps. One of them may be sick. Compare voltages between the two. Swap tubes between the two. Be sure the TRS jack is working properly. Should be an easy fix.

     https://el34world.com/charts/Schematics/files/Gretsch/Gretsch_6169_FURY_Piggyback.pdf

[TubeGeek]

I should've added more info...


The linked schematic is the one I have been using throughout this job. I feel like I have it memorized at this point.



I built a speaker cable assembly with a 1/4" TRS jack to plug into the main output on the chassis.  The 1/4" TRS jack goes to a female 1/4" mono jack and a regular 1/4" male plug.


I have two speaker cabinets hooked up as well.


One speaker sounds good and "normal". The other has barely any output power.  I can hear it if I put my ear right next to the speaker but it's drowned out by the main output speaker.


I tested both sets of power tubes and one side is definitely not great but still functional.


I installed two sets of my bench test tubes and I still get weak output on one side.


I'll be looking closely at this tonight...possibly an OT problem...

[shooter]

do you have 28-30vdc on BOTH sides of PA cathodes?
did you swap speaker connections AT the speaker to "verify" it ain't the harness or speaker?

[TubeGeek]

do you have 28-30vdc on BOTH sides of PA cathodes?
did you swap speaker connections AT the speaker to "verify" it ain't the harness or speaker?

Yes, I measure 28 on one cathode pair and 31 on the second pair.


I'm pretty sure the harness is correct but I am going to verify this when I get to it later tonight.


The speaker isn't the issue as I am using my known good test speakers to do this.  I do not have the original speaker cabinet that was made to pair up with this amp.

[sluckey]

I'm pretty sure the harness is correct but I am going to verify this when I get to it later tonight.

This is my #1 suspect.

[TubeGeek]

I'm pretty sure the harness is correct but I am going to verify this when I get to it later tonight.

This is my #1 suspect.

I swear I did not use conductive rubber mat in it.

[sluckey]

James, post a couple really hi-rez pics that clearly show everything that I'm showing in these two little pics. I don't need to see anything else so zoom in real close and crop everything that ain't in my little pics. If possible, I do want to see all the lugs on the jacks in both pics. It looks like someone has added a second mono speaker jack in the "left" pic. That could be a factor.

In the left pic I think I see the green OT wire connected to an unused pin on a 6L6 socket. Also on that same unused socket pin is a green wire that goes to the TRS jack near the fuseholder. Also on that same unused socket pin is a yellow wire that goes to the additional speaker jack. I want to be able to confirm all this.

[TubeGeek]

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[TubeGeek]

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[TubeGeek]

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[TubeGeek]

James, post a couple really hi-rez pics that clearly show everything that I'm showing in these two little pics. I don't need to see anything else so zoom in real close and crop everything that ain't in my little pics. If possible, I do want to see all the lugs on the jacks in both pics. It looks like someone has added a second mono speaker jack in the "left" pic. That could be a factor.

In the left pic I think I see the green OT wire connected to an unused pin on a 6L6 socket. Also on that same unused socket pin is a green wire that goes to the TRS jack near the fuseholder. Also on that same unused socket pin is a yellow wire that goes to the additional speaker jack. I want to be able to confirm all this.

The mono jack looks original as I see labelling on the chassis saying ext speaker. It never occurred to me that it is not on the schematic.


Tracing this and the other jack wiring now…I have a feeling you're right on something here being wonky.


In the left pic I think I see the green OT wire connected to an unused pin on a 6L6 socket. Also on that same unused socket pin is a green wire that goes to the TRS jack near the fuseholder. Also on that same unused socket pin is a yellow wire that goes to the additional speaker jack. I want to be able to confirm all this. 

Yes, you are correct about this.

[TubeGeek]

Harness:


I made this harness to do my own testing while repairing this amp.


The idea is to use the TRS 1/4" plug on the main speaker output, to match the jack on the amp chassis. It's a Y cable of sorts…


The output of the TRS plug goes to a regular mono 1/4" plug that will be used to connect to the main speaker cabinet that the amp head will sit on.  The owner of this amp does not have the original speaker cabinet made for this amp head. 


I was thinking of using two separate speaker cabinets, both with an 8 ohm 1x12" speaker. That way both output sections of the amp are used simultaneously.


The second output of the Y cable goes to a female 1/4" jack.  This allows a second speaker cabinet to be plugged in.  I'm using a 10 foot speaker cable (1/4" - 1/4") to another cabinet in my shop.


Maybe I have this all wrong   

[TubeGeek]

What about using a switched ground 12a jack on the ext speaker output?  Would that help?

[sluckey]

If it were my amp, I'd replace those two speaker jacks with two Switchcraft 12A jacks. Put a jumper between the ground lug and switch lug of both jacks so the tip will be shorted to ground if nothing is plugged in. Then you can just use two simple speaker cables and there will be no more confusion or special dongle to keep track of.

even better... Put a 8Ω/25W resistor between the ground lug and switch lug of both 12A jacks.

BTW, it is possible that one of the OT has been damaged due to someone not using the proper speaker cable or just not understanding what's going on with those jacks.

[TubeGeek]

The funny thing is I thought about doing this when I initially started looking into the speaker output Jack on this amp.


It seems so obvious now.

Yes that’s something I have a suspicion about is whether one side of the output has been damaged because it hasn’t been used properly. I don’t know why, but I have a gut feeling. There could be a problem with the output transformer on one side.


I will replace those jacks and report back.

[TubeGeek]

Replaced the jacks.  One of the OT's is bad. Hardly any output coming from one side.


Now on the hunt for a suitable replacement...

[TubeGeek]

Thoughts on a Hammond 1650FA as a replacement?


25W— 7600 ohm CT —128mA


The size looks very close, possibly a direct fit without drilling new holes.

[WimWalther]

Replaced the jacks.  One of the OT's is bad. Hardly any output coming from one side.

Have you compared DCR measurements between the two OTs, just to double-check your fault finding? You can also inject AC (via Variac or funct gen) into the pri. and read voltage on the sec. to compare.

Another thought.. unless you can find an ideal match, it might be better to replace both OTs with identical new units and save the pull for a later repair or project?

Or.. do away with the goofy dual-OT setup, and convert to a single 50-75W output, all four 6L6 on one OT. Those are 6L6GC, are they?

[sluckey]

Thoughts on a Hammond 1650FA as a replacement?

That sounds more like a good choice for a 6V6 amp. I would not use it. The Hammond 1760J is a good choice for that amp. Only cost $60.40 at Hawk Electronics. I bought a 1760J from Hawk for my Phoenix amp. Good OT and best price I've found on the net. Hawk is showing the wrong pic on their website. The 1760J looks like my pic below.

[TubeGeek]

Replaced the jacks.  One of the OT's is bad. Hardly any output coming from one side.

Have you compared DCR measurements between the two OTs, just to double-check your fault finding? You can also inject AC (via Variac or funct gen) into the pri. and read voltage on the sec. to compare.

Another thought.. unless you can find an ideal match, it might be better to replace both OTs with identical new units and save the pull for a later repair or project?

Or.. do away with the goofy dual-OT setup, and convert to a single 50-75W output, all four 6L6 on one OT. Those are 6L6GC, are they?

That's a great idea, regarding the larger single OT.  I ran it by the owner and he declined.  He wants to keep it as original as possible. He is mulling over getting two new OT's but I suspect he will only go with one.


Yes, two pairs of 6L6GC's.


I'll be testing the suspected faulty OT soon.  Hopefully this weekend.  I have another bench OT I am going to wire in place to confirm.

[TubeGeek]

Thoughts on a Hammond 1650FA as a replacement?

That sounds more like a good choice for a 6V6 amp. I would not use it. The Hammond 1760J is a good choice for that amp. Only cost $60.40 at Hawk Electronics. I bought a 1760J from Hawk for my Phoenix amp. Good OT and best price I've found on the net. Hawk is showing the wrong pic on their website. The 1760J looks like my pic below.

Thanks for the recommendation. I see I can get these in Canada for $100.  Easier to order here and not pay extra duty/tax/brokerage bs I have to pay up here.

[TubeGeek]

Confimred one of the original OT's in the gretsch shorted out.  I measure 9 ohms on one side from the CT and 77 ohms on the other.


The good gretsch transformer measure 77 ohms on both sides of the primary windings from CT.


I think the owner of the amp is going to have me order two new one's.  I may get to keep the original OT if I discount my labour installing the new ones.

[WimWalther]

Confimred one of the original OT's in the gretsch shorted out.  I measure 9 ohms on one side from the CT and 77 ohms on the other.


The good gretsch transformer measure 77 ohms on both sides of the primary windings from CT.


I think the owner of the amp is going to have me order two new one's.  I may get to keep the original OT if I discount my labour installing the new ones.

Good work, the resistance readings cinch the deal. Too bad.. as you suggest, it may be the result of misuse due to the odd output section scheme.

A pair of new OTs would really be the Better Idea, IMHO. I'd steer the cust to make that decision.

Discount your work? Well, maybe.. but really, he ought let you keep the pulled OT as a small gratuity for such accurate & thorough diagnosis!

After all, if he knew what to do with it, you'd not have to fix his amp for him! ;-)

[TubeGeek]

Update:


New OT's arrived and I have installed them.  I didn't have to drill new holes in the chassis for the OT's.  I mounted them on an angle and yes, I did verify they wouldn't cause any hum issues before deciding to go this route.  The amp sounds really good to me.  I dig it.  The tremolo sounds nice too.  It's fun having two speaker cabinets across the room, sounds "fuller".


I installed 8 ohm 25W resistors on each output jack as well for safety. Don't want the owner to cook these new OT's.


Hopefully I can button this amp up and send it on its way.  Have a bunch more waiting behind it.