But I have done it! The amp sounds great. Some contact cleaner, a 3 prong mod and then I’ll button up the cab and give it a final run through, but I think I finally got it.
I’ll save the final bit for last, because I want to do a quick walk through all the steps it took.
- Received Amp, turned it on, loud hum with volume at 0 and nothing in the jack.
- Opened back and found missing 6X4 rectifier with two shitty diodes instead.
- Ripped out diodes, compensating resistor and death cap, plugged in 6X4. Same hum.
- Replace all of the filter caps with 500v rated caps. Lost hum at zero volume. Hum now follows volume knob with or without input.
- Scope traced a reference signal and isolated signal issues to output pin of power tubes.
- Tried different power tubes. All is well.
The very first step I took was to swap out tubes but that didn’t help. It didn’t occur to me to try the tubes again after step 4 because I had already tried that. It didn’t occur to me to start from the beginning … but that was the right call. I could have fixed this without the scope, but that’s ok, because it was definitely fun to trace the signal.
In retrospect, I notice that I had even commented that all of my tubes could be suspect because they had been used in the amp with diode rectification and could be cathode stripped.
If I would only listen to voices in my head…
I have a GA-5 Skylark Crestline and need to install a new speaker. I’m not sure how many ohms as the current speaker (Quam- probably not the original?) does not indicate. I can’t find a schematics for the Crestline models with the ohms listed. Other GA-5 amp schematics and parts lists indicate 8 ohm speaker but I came across a harmony central user review where someone states that his Crestline had a 4 ohm Gibson Ultrasonic speaker: http://reviews.harmony-central.com/reviews/Guitar+Amp/product/Gibson/GA-5+Skylark/10/1. Would you happen to have this information? Thanks.
Weird.. first person I’ve ever heard describe any Gibson speaker as 4 ohm. As luck would have it, I just modded the amp for spkr out and amp in jacks.
Now.. measuring the DC resistance is not the same thing as measuring the Impedance, however, when you want to know the nominal (rated) impedance, it is sufficient.
Mine is the original gibson ultrasonic and it is 8 ohms. I can’t find my copy of the Gibson MSM on this machine but I’ll double check to see if there is any more info there.
It’s 8 ohms but a good second opinion could be had at https://taweber.powweb.com/weber/
He’ll probably get right back to you. Be very specific about the amp, schematic and tube set. Of course, it’s the OT that defines what is needed, but he’ll need that info to be sure you are talking about the same circuit.
I’m just becoming more familiar with Weber recently and intend on using one of their speakers in my Skylark Crestline. Any experience with the Chicago Vintage Series? Anyway, I have heard the stories about how responsive Weber is and it sounds like they run a fine operation- quality at a reasonable price with good service.
I’m working with a professional that mostly services old radios for getting this Skylark up and running, as I am new to this and have a healthy fear of death by electrocution. I am a novice and he has been kind enough to take the time and show me a few things.
Thanks for your info help and advise re: a second opinion- it is much appreciated. I’ll let you know how things progress.
No but I’m looking forward to your results, as I think my speaker is blown on one of the skylarks.
The EA-50T is a virtual clone of the Crestline Skylark GA-5T which is 8 ohm. The MSM doesn’t show rating for the EA-50 (GA-5) but the power circuit is identical so you can be sure that 8 ohms is right.
I’ve put in an order for a Weber CVC10. I know it’s not alnico, but i think it should do the job just fine. Don’t want to sink too much money into this just yet :)
I recently got an Epiphone EA50 (same circuit as Gibson GA5 Crestline). I also got a 1970 Fender Bronco (Vibrochamp) about the same time. Have done a cap job in both and replaced some tubes, both sound pretty good. I put a Weber 10″ alnico (10a100t) vintage series in the Epi and it really increased the volume. I actually like the tone a little better on the stock speaker, but it’s not very loud and already starting to tear on the cone a little. The Weber gave this a more open sound and a bit more bottom. It’s still really bright though. Can work around the brightness with tone control on a TS808. I guess I like the sound of the Epi better than the Fender, but in fairness I haven’t tried the Fender with a decent 4ohm speaker.
Question:As you know the EA50 has no tone controls – did you make any mods to the resistor or cap values on the volume control that tamed the treble or improved the tone?
thanks
I did not make any circuit changes. I brought everything to spec.
I’m about to try the Weber 10A125 myself. I will write it up when I do. The volume increase is no surprise, to be sure.
What don’t you like about the tone?
I have a simlar Skylark and I love the amp. I have had some noise issues and most of my issues were resolved by installing a grounded plug. The capacitors have been replaced with a couple of Nicholsons. Not sure if the Spragues would have made it quieter. I am trying to locate some Spragues. Still some static type noise above 6 but pretty quiet below that. Tubes have made a difference, the one tube I am shy is the 6EU7 and I have ordered a new one. I am curious about your opinions of the Weber 10″ ceramic speaker. I have been thinking of swapping out the stock 10″ with the Weber product.
Mark
I got the weber 10A125 which is AlNiCo.
Clear, crisp and significantly louder and it fixed the lack of definition in the lows. It sounds very good.
However, I preferred the old sound. It was smoother and creamier, if I may be so bold as to put it that way.
I’ll likely recone and old speaker, keep an old speaker as is and then taste test all three.
I have some low volume noise that my mic is picking up so I’ll be back in the damn thing soon enough.
I have a 63 ga 5t and she looks pretty good, not beat up at all. sounds great overall but the tremolo won’t work. any idea what this would be? thanks
Hey.. sorry I didn’t get back to you quicker. Can you be more precise about what happens?
The tremolo is 1/2 of V2 (from the back the second to right 6EU7) You could switch the two (V1 and V2) to see if that changes anything.
Or better yet, if you have another tube, swap it in. If that doesn’t help, you probably would have to start looking through the discretes in there.
They have a great Trem when it works.