Had the opportunity to work on an old Tweed Champ this weekend. Belongs to a friend who plays harp in a local band of some note, The Muddy Basin Ramblers.
http://www.muddybasin.com/
The Ramblers play all over Taiwan, and as Conor (owner of the amp) found out the hard way, sometimes the stage wiring leaves a bit to be desired. In this case, a high voltage outlet (220 +) looked the same as the regular 112 VAC outlets. This happened about six or eight month ago and another buddy had already determined the only damage was to the main filter caps and fuse. He removed the blown caps, but didn't have replacements. This weekend Conor brought the amp over along with a very long three prong chord he hoped to have installed. After replacing the main filter caps (used 20, and two 10's rather than the 16 and two 8's as that's all I had). The amp volume seemed too low and distorted. It still had the original 25 UF cathode bypass caps. Both had drifted way up and one had a really high ESR. I replaced those with sprague 25 uf's and that helped alot. The preamp tube is relatively new JJ 12 AX7, trying other tubes in that spot didn't do much to the overall volume. The power tube may be original, its an old Sylvannia. It's a bit worn, swapping in a modern EH (all I had on hand) was a big improvement. The rectifier tube looks to be the original RCA - glass is little loose in its base, but it's putting out the right voltage even under load.
Three prong cable installed - will be checking it over this week when I have a chance.
Not much to the circuit, but I guess I can check the resistors and tension/clean the sockets. Has the blue Ajax coupling caps, no DC leakage noted. I know their are some mods that can be done to make this amp a bit more harp friendly, but couldn't bring myself to molest such an old amp. prefer to leave it stock. Will leave the original caps in bag in the amp. Maybe, someone else will want to put the modern cap in those old paper shells for appearance sake.
Fun little amp.
Mike
Tweed Champ
Moderators: pompeiisneaks, Colossal
Tweed Champ
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Sunnydaze
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Stevem
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Re: Tweed Champ
Yup!, only some 3.5 watts in that bugger!
If you change to power supply dropping resistor to get the first gain stage down to 80 to 90 volts on the plate the amp will grind a lot better for harp and the un-needed highs rolled off will make for less feedback from his Harp Mic also!
If you change to power supply dropping resistor to get the first gain stage down to 80 to 90 volts on the plate the amp will grind a lot better for harp and the un-needed highs rolled off will make for less feedback from his Harp Mic also!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Tweed Champ
I thought a little about lowering the voltage on the pre-amp, also increasing the grid resistor on the input jack to make it a bit more harp friendly.
Still, even now, the preamp already compresses half the wave at about 4 on the volume pot. Kind of surprised me a bit.
Conor is definitely more of a player than a collector, will talk to him about it.
Mike
Still, even now, the preamp already compresses half the wave at about 4 on the volume pot. Kind of surprised me a bit.
Conor is definitely more of a player than a collector, will talk to him about it.
Mike
Sunnydaze
Re: Tweed Champ
Maybe remove the death cap off the mains fuse as well?
Re: Tweed Champ
Yup, did that when I put the three prong cable in. threw that in his original parts bag - blue Ajax .047.Colossal wrote:Maybe remove the death cap off the mains fuse as well?
I just AB'd against my silver face Bronco (vibro champ) Bronco is louder and a little brighter/cleaner both sound good.
A Strat straight in, what a blast!
Mike
Sunnydaze
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Tweed Champ
Yeah, the silver face amps have over 400 volts on that poor 6V6!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Tweed Champ
Hello Steve,
One nice thing about Taiwan is the wall voltage is 112 VAC compared to the much higher current US voltages. So my Bronco is not running at 400 - it's in the the 370's (I think) - been awhile since I bothered to to open it up. Sweet little amp, and can sound pretty large when mic'd up.
The lower wall voltage in Taiwan helps the old amps run closer to their original specs, and in most cases, runs the heaters a little on the low side - all good things.
Mike
One nice thing about Taiwan is the wall voltage is 112 VAC compared to the much higher current US voltages. So my Bronco is not running at 400 - it's in the the 370's (I think) - been awhile since I bothered to to open it up. Sweet little amp, and can sound pretty large when mic'd up.
The lower wall voltage in Taiwan helps the old amps run closer to their original specs, and in most cases, runs the heaters a little on the low side - all good things.
Mike
Sunnydaze
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Tweed Champ
I most times run a 5V4 recto in mine unless I want a lot of clean power and then the 5Y3 goes in along with a JJ 6V6 and all stays well!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Tweed Champ
Wondering if there is a problem with the OT on this Champ. Take a look at the attached scope shot.
The yellow trace is measured at the output transformer secondary on a dummy load. The blue trace is the output transformer primary taken from the 6V6 power tube plate. Injected signal is a 1000hz from an app on my iPhone.
Aside from the very low clean output level, the indicated transformer turns ratio looks really high to me.
As you can see from pic, when the OT primary voltage is about 59.3 VRMS, the secondary is about 1.14 VRMS. Means the indicated turns ratio is about 52, squared = 2,705. At the spec'd 4 ohm speaker load that's a reflected impedance of about 10,800. I double checked the voltages with my DMM and got very similar results (diff by a few mv).
Other voltages in the amp are pretty close to expected values, and it sounds OK. Tried several power tubes, and not much difference in indicated ratio or voltages.
Not sure what I should be seeing, or whether there is a problem here.
Today is a holiday in Taiwan - 10 - 10 day. Taiwan independence from Japan occupation, so had a bit of time to fool around with this thing.
Would appreciate any comments or guidance.
thanks & best regards
Mike
The yellow trace is measured at the output transformer secondary on a dummy load. The blue trace is the output transformer primary taken from the 6V6 power tube plate. Injected signal is a 1000hz from an app on my iPhone.
Aside from the very low clean output level, the indicated transformer turns ratio looks really high to me.
As you can see from pic, when the OT primary voltage is about 59.3 VRMS, the secondary is about 1.14 VRMS. Means the indicated turns ratio is about 52, squared = 2,705. At the spec'd 4 ohm speaker load that's a reflected impedance of about 10,800. I double checked the voltages with my DMM and got very similar results (diff by a few mv).
Other voltages in the amp are pretty close to expected values, and it sounds OK. Tried several power tubes, and not much difference in indicated ratio or voltages.
Not sure what I should be seeing, or whether there is a problem here.
Today is a holiday in Taiwan - 10 - 10 day. Taiwan independence from Japan occupation, so had a bit of time to fool around with this thing.
Would appreciate any comments or guidance.
thanks & best regards
Mike
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Sunnydaze
Re: Tweed Champ
IMO there's just too much chance that touring w/ that amp it'll get stolen, maybe they don't do that in Taiwan, but I doubt it.
Unless vintage equipment is part of the the band's vibe, you should whip up a clone for him, I've had great luck cloning Champs they're easy to get right, even vintage coupling caps are easy as you only need two, you can hunt old molded caps on ebay they don't need to be Ajax or Astrons, blacks, reds, greenies all sound good, grab a couple extra and find two good ones. You have to get the voltages right though ~360V plates w/ the 470R at ~40ma. Only hard part is the speaker. If you do it, the mojotone multi tap PT I used ran a bit high, but might be spot on at 110V. Anyway, just a thought.
Unless vintage equipment is part of the the band's vibe, you should whip up a clone for him, I've had great luck cloning Champs they're easy to get right, even vintage coupling caps are easy as you only need two, you can hunt old molded caps on ebay they don't need to be Ajax or Astrons, blacks, reds, greenies all sound good, grab a couple extra and find two good ones. You have to get the voltages right though ~360V plates w/ the 470R at ~40ma. Only hard part is the speaker. If you do it, the mojotone multi tap PT I used ran a bit high, but might be spot on at 110V. Anyway, just a thought.
Re: Tweed Champ
Thanks RP.
No doubt I could quickly build him something that would probably sound better for harp.
This one's not completely vintage, you can see the Jensen Mod speaker from the pics, and the power transformer looks like a replacement. Taiwan is a pretty safe place, and the amp is small enough to stash away between sets.
I have a more than full time job and fool around with amps as a hobby. I'll be compensated for this job with a bunch of beers at one of the local pubs.
Curious about this output transformer though. The turns ratio is kind of what I'd expect from a reverb driver like used in a Deluxe (reflects around 22,000 w/ 8 ohm load). This one is just under 11,000 with a four ohm load.
Thanks
Mike
No doubt I could quickly build him something that would probably sound better for harp.
This one's not completely vintage, you can see the Jensen Mod speaker from the pics, and the power transformer looks like a replacement. Taiwan is a pretty safe place, and the amp is small enough to stash away between sets.
I have a more than full time job and fool around with amps as a hobby. I'll be compensated for this job with a bunch of beers at one of the local pubs.
Curious about this output transformer though. The turns ratio is kind of what I'd expect from a reverb driver like used in a Deluxe (reflects around 22,000 w/ 8 ohm load). This one is just under 11,000 with a four ohm load.
Thanks
Mike
Sunnydaze
Re: Tweed Champ
I turned the web inside out trying to get exact info on the orig 5F1 OT, 5K? 8K? unchanged through '50s-'70s? Sames as the one's in the stand alone reverbs? Not a single post by anyone anywhere who actually measured one.sunnydaze wrote:Curious about this output transformer though. The turns ratio is kind of what I'd expect from a reverb driver like used in a Deluxe (reflects around 22,000 w/ 8 ohm load). This one is just under 11,000 with a four ohm load.
If that one is its original and working right I'm also curious that it's 11K. If it is damaged it could only go down not up, only short to less winding, right? It used a common generic, I think Triad OT, that were in all sorts of things, some TV repair guy 40 years ago could have grabbed whatever was handy that went right in, or a BF reverb replacement, you'd never be able to tell at this point. IIRC the tweed champs didn't have bells, but they made them into the early sixities so not sure.
My best sounding Champ has the Allen OT - 7K? w/ 4 & 8R out, which is really useful in a champ, they sound killer through a bigger cab, a bigger speaker is about the only way to brighten it up, tweaks go nowhere. If you need to replace it maybe give the Allen a try, check first, but many of his OTs are fat-stack types but with drop-in dimensions. Assorted vintage Triads show up often enough.
http://www.ebay.com/itm/Triad-S-7X-Outp ... 2ed7864569
I never pass up a chance to build a Champ. Even if you're busy it's an evening's work, most effort & time is putting the parts together. Doesn't you pal need a back up
Re: Tweed Champ
Thanks RP.
I did a lot of searching on the net too, and got the same results as you. Hammond's replacement is 7k
http://www.hammondmfg.com/guitarLineOT.htm
Classictone's has a dual primary 5K & 8K.
http://www.classictone.net/40-18030.pdf
Like you, I couldn't find anything definitive on what was actually used in these old tweeds. Before I measured it, I was expecting the result to be in 7K - 8K range.
This one is pretty similar to what I would expect from a reverb transformer.
Glad you also think a short would cause the opposite problem, or rather could only short to lesser windings. That is what I was thinking as well. Thinking about a little more, I guess if the short were on the secondary side, could cause a higher indicated turns ratio.
I'd be happy to build him another amp if he wants.
The chassis is already back in the cabinet, but I may be able to check the part number on the OT.
Thanks & best regards,
Mike
I did a lot of searching on the net too, and got the same results as you. Hammond's replacement is 7k
http://www.hammondmfg.com/guitarLineOT.htm
Classictone's has a dual primary 5K & 8K.
http://www.classictone.net/40-18030.pdf
Like you, I couldn't find anything definitive on what was actually used in these old tweeds. Before I measured it, I was expecting the result to be in 7K - 8K range.
This one is pretty similar to what I would expect from a reverb transformer.
Glad you also think a short would cause the opposite problem, or rather could only short to lesser windings. That is what I was thinking as well. Thinking about a little more, I guess if the short were on the secondary side, could cause a higher indicated turns ratio.
I'd be happy to build him another amp if he wants.
The chassis is already back in the cabinet, but I may be able to check the part number on the OT.
Thanks & best regards,
Mike
Sunnydaze
Re: Tweed Champ
I went ahead and pulled the chassis and took pics of the transformers.
The power transformer is part number 125P1A with code 606207.
The output transformer is part number 125A3A with code 606-2-07.
That code could mean the 7th week of 1962.
The OT part number matches the Hammond and Classictone reference numbers.
Maybe both are original.
Question: I measured the turns ratio while it was connected to the power tube, with a signal injected. Would that distort the measurements? I did vary the HZ's on the injected signal from 120 HZ all the way up to 2000 HZ. Didn't make much difference.
Thanks & best regards,
Mike
The power transformer is part number 125P1A with code 606207.
The output transformer is part number 125A3A with code 606-2-07.
That code could mean the 7th week of 1962.
The OT part number matches the Hammond and Classictone reference numbers.
Maybe both are original.
Question: I measured the turns ratio while it was connected to the power tube, with a signal injected. Would that distort the measurements? I did vary the HZ's on the injected signal from 120 HZ all the way up to 2000 HZ. Didn't make much difference.
Thanks & best regards,
Mike
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Sunnydaze
Re: Tweed Champ
Little traffic on this post but I find that your very original looking OT is 11K pretty darn interesting. You have the honor of being the first since the internet happened to have done this, apparently. Could it really be 11K? 6V6GT data sheet says 5-8.5K but preety sure I've seen 10K OTs recommended for SE 6V6. Did Fender care so little about it's basic student amp that they just used whatever Triad or Schumacher had in stock? Sure would be nice to hear from others on this Champ oddness. Is this the tranny from the brown Reverb units? Looks like 8K is more accurate that 5k, maybe that's why I like the 7K Allen.
I'm not one of the savants here but I believe the way you are measuring is the more accurate way. I've always just hooked up to a variac with 5V or the 6.3 volt tap of an other tranny, on the sec, with 2 meters and just did the math. It's accurate enough as it always got me what the OT was supposed to be.
Don't know why yours isn't very loud. BTW you like the Mod in there? I didn't, but I can't recommend an 8, I didn't like any I tried, settled on a Weber Ceramic Blue Dog as I wasn't going to buy anymore 8s, found it a bit crisper, better defined distortion than the MOD.
I'm not one of the savants here but I believe the way you are measuring is the more accurate way. I've always just hooked up to a variac with 5V or the 6.3 volt tap of an other tranny, on the sec, with 2 meters and just did the math. It's accurate enough as it always got me what the OT was supposed to be.
Don't know why yours isn't very loud. BTW you like the Mod in there? I didn't, but I can't recommend an 8, I didn't like any I tried, settled on a Weber Ceramic Blue Dog as I wasn't going to buy anymore 8s, found it a bit crisper, better defined distortion than the MOD.