To 'Bay or not to 'Bay: Thunderbird Auction

gilded

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Gentlemen (and Coastie),

Okay here's a T'bird amp on the 'Bay with changed out speakers & possibly a changed out baffle-board (it's pine-plywood and not particle board-that's a change, right?).

http://cgi.ebay.com/VERY-RARE-1968-Guil ... dZViewItem


It has one 15" speaker and two 8" speakers.

I want a T-bird real bad.....I love my Thunder 1 RVT but I'd like some headroom.
Do you guys think I ought to go for it, or wait for a cleaner one?
How much should a guy pay for a non-orig T'bird, for that matter??

thanks, gilded
 

capnjuan

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gilded said:
...T'bird amp on the 'Bay with changed out speakers & possibly a changed out baffle-board (it's pine-plywood and not particle board-that's a change, right?). John K has 2 of these but my understanding is that a plywood baffleboard is a replacement; if there are really 2 - 8" speakers, it would have had to have been changed.

It has one 15" speaker and two 8" speakers. Seller sez: "This amp’s reverb works off of 2- 8” speakers, not a spring reverb tank." Need a comment from John K here, but I guess this model generates the echo function electronically off the reverb amp pc board dispensing with the tank.

I want a T-bird real bad.....I love my Thunder 1 RVT but I'd like some headroom. Nothing's perfect...

Do you guys think I ought to go for it, or wait for a cleaner one? Your ability to do some of the fix'-em-up offsets some of the risk. These go better when you understand it to be a partial 'project' on the go-in. You might ask the seller if he did the speaker changes and why. I don't know what he was trying to accomplish with the 2nd 8" speaker.

How much should a guy pay for a non-orig T'bird, for that matter?? These amps have been running $225 - $275 for average condition on eBay; I can't say that I've seen an especially clean one on eBay .
Hi Gilded, hope this helps. As ever, used tube gear unless well-maintained, nearly always need a cap job - $125 - $175. So often, people sell them because they don't think they can recover the tech-expense in the auction.

Good luck!
 

gilded

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capn,

First off, thanks (as always) for the input.

I'm curious. When you say, "I guess this model generates the echo function electronically off the reverb amp pc board dispensing with the tank", do you have any information that the Guild amp designers ever did anything like that on any of their amps?

You see, I thought that possibly the seller might actually be saying something like you are talking about (although I could never have couched the words as elegantly as you did!), but it also occurred to me that perhaps they didn't have a clue what they were talking about, too.

I wonder if the seller's representation that 'there is no reverb tank' is indicative of the fact that the former owner might have removed the reverb tank and used the reverb section as an additional power amp for the two 8" speaks?

It could also be that he is just inarticulately trying to explain the purpose of the 8" speakers, or that the reverb tank is built into the chassis and he doesn't see it. In fact, maybe the question to ask John Kidder about is whether he knows if the tanks were ever installed in the amp chassis as opposed to the bottom of the cab (like in my Thunder 1 RVT)?

Whatever the case is, I guess I need to contact the seller and ask for a better description
and maybe some additional pics.

I think the current seller got the amp out of an estate. I believe the original owner
did all the mods. As for why an extra speaker, 'more speakers is betterer', right?

As for price, well, nobody ever wants to get 'upside down', pricewise, in an amp, but we're all chasing tone, not necessarily profit. Sometimes, you just have to take the hit on a cap job and see how the darn amp sounds, especially a relatively rare amp that many knowledgeable people say sounds really good. That's how I rationalize the extra bucks, anyway.

cheers, gilded

PS Coastie, thanks for fixing up the link to eBay.
 

capnjuan

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Hi Gilded: this may be more than you need to know but here goes. Pic below is a fragment from the Thunderbird schematic. The blue box on the right shows how the reverb tank - center right edge - is connected to the output side of the transformer. The reverb signal, in yellow, is taken from the transformer at the top and through a capacitor and resistor in series. I'm not completely sure but I think the cap knocks down some bass to keep the reverb input from being too 'muddy' and the resistor matches the 'impedance' of the inbound signal to the input impedance of the can. The signal continues to the 12AX7 where the yellow line stops.

tbirdreverb.jpg


In the T1 RVT, the signal is separately tapped from the preamp and, if reverb was switched off, that signal was still seen and amplified by the 6BM8 output tube and sent, via another transformer, to the 8" speaker. By contrast, in the Thunderbird, there is no signal leg from the preamp ahead of the reverb can; only a signal taken from the primary output transformer (in yelow) and tied to the input of the 12AX7. (The numbers in circles at the reverb amp are the connections to the power supply; not shown) In the Thunderbird and if the reverb is switched off, the signal coming from the reverb can / first 12AX7,is grounded by the footswitch; that is, when switched off, there is no signal appearing on the reverb 6BM8 and the 8" speaker does nothing.

Sooooo; I question this statement: "This amp’s reverb works off of 2 - 8” speakers, not a spring reverb tank." There are circuits that can create delay / echo however this design includes a spring reverb (4G is the Hammond Gibbs ID#). If there is no reverb can in this amp, then the reverb amp is wired directly to the primary output transformer. Unless the reverb amp has been completely reworked, the only way to get an 'echo' would be to wire a device (resistor network?) between one of the two 8" speakers to 'delay' the signal arriving at the 2nd speaker.

Giving Auction Boy the benefit of the doubt, he may just be going by what the seller told him. If he is, in fact, a real-time music store dealing in amps, he knows perfectly well this is a 'project' or cares too little to confirm what he was told. Assuming it hasn't been tortured, this amp could probably be rebuilt but, unless you're going to do it or you have an amp tech friend who owes you money ... a think a pass might be in order.
cj
 

JazzWest

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Hard to say until you get the amp, open the chassis, and make sure that the mods, if there are any, are reversible. That is if you're plan to restore it? Sounds like the seller is no technically inclined to verfiy some important details? Overall looks good and worth it for the right price? These Thunderbirds are much more "bulky" to lug around...

On your T1 RVT..., why not try swapping out your current with a JBL D120 or equivalent (i.e. Weber Calif 12") as well as a Weber Sig 8 for the reverb"? Also you can try one of Weber's Copper Caps to replace the Ez81 rectifier. Being a solid state device, emulating a rectifier, they do "tighthen" up output.
 

capnjuan

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JazzWest said:
why not try swapping out your current with a JBL D120 or equivalent (i.e. Weber Calif 12") as well as a Weber Sig 8 for the reverb"? Also you can try one of Weber's Copper Caps to replace the Ez81 rectifier. Being a solid state device, emulating a rectifier, they do "tighthen" up output.

Hi JazzWest and welcome: do you have a T1 RVT? The usual 'knock' on this amp is a lack of headroom; do you think a speaker upgrade would help that? Don't disagree about the Copper Cap rectifier; might make the output a little 'stiffer'.

cj
 

capnjuan

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Bump: another Thunderbird for sale in an eBay store, Hitch 'em up tight boyz, BIN at $899: link to eBay Thunderbird here

My editing of seller's ad text: "This amp features Reverb and tremolo with a separate 8 inch CTS speaker for the reverb. However there is no tank in so the reverb is not working. The suggestion is that if it had a reverb can, it would work but it doesn't say that. The amp is all original probably including the tubes. The seller is saying that the tubes are original if they are. The amp includes original 2 prong power cable and the original foot switch. That the power cord is original isn't a positive, it's a negative. This works besides the reverb with a pretty decent volume. Pretty decent? It may need serviced to make it sound its absolute best, which will be awesome! The seller is saying it will sound good if it does.

WKRaP in Cincinnati (actually across the river in Covington KY) and for big money; why pay less?


guildtbird.jpg
 

gilded

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Cap'n, JazzWest,

Lots to think about. Thanks!!

I saw the Ky. amp, too. Another prize!

As for a speaker upgrade helping with the headroom? Cap'n, I think I get it......here's what comes to mind:

I've had four blackface Fender Pro Reverb amps over the last 30+ years and have thought of them as punier-sounding than a
2 6L6-GC powered amp should sound. I have blamed both the medium-grade speakers and the munchkin-sized trannies.

In fact, one amp builder from the '90's told me that the Pro Reverb 'fix/ was either better speakers or a stouter Output Transformer.

Eventually, I 'tried that speaker replacement fix' in the sense that my third Pro had factory JBLs. It was a fantastic amp, maybe the best sounding amp I ever had (versatile, too, except it couldn't do the Super Reverb 'spaghetti western' sounds that SRs seem to get with 4 10" stamped frame speakers that 'give' ever so slightly). Still, it weighed 67 lbs and hurt my back every time I carried it from the car to the house.

My last Pro was the runt of the litter (cab stripped of tolex and painted with pink speckled paint, replacement Power Trannie and Rola replacement speakers). In the process of restoring it, I did a cap job and it sounded okay, but not great. Then, I put some exc. condition Jensen '65 C12-N speakers in it. It sounded absolutely incredible.

So, I think speakers can make a big difference IF they are more efficient, giving you more dBs per output watt.

Having said that, I think D120s weigh around 16 pounds each. That's a lot of weight to be hanging off the thin, particle-board speaker baffle in a Thunderbird or a Thunder 1 RVT. Hmmn, maybe an efficient Neo speaker with a super-light magnet and correspondingly less frame weight would work in this application?

On a final note, I know there are several different variations of Thunderbird; 1x12 & 1x8, 2x12, etc.
Is there one variety/generation/year that people prefer over another?

gilded
 

capnjuan

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gilded said:
I saw the Ky. amp, too. Another prize! See below.

As for a speaker upgrade / the headroom? Well, efficient speakers and good transformers are 1/2 the equation; the other 1/2 is manipulating the plate voltages and cathode caps in the preamp to increase the output voltage seen by the output tubes and down-sizing the coupling caps ahead of the outputs to 'dirty' the amp's signal - make it stop trying to sound clean.

I think of the T1 as an example of attempt by Guild to cross a clean/jazz amp with a R&R amp however it has a fairly small, mid-60s OT. I put a Celestion 12" Greenback / 8" GL in Coastie's T1 but left the circuit stock; it is what is it and I wasn't asking it to be something it wasn't.


Eventually, I 'tried that speaker replacement fix' in the sense that my third Pro had factory JBLs. It was a fantastic amp, maybe the best sounding amp I ever had ......Still, it weighed 67 lbs and hurt my back every time I carried it from the car to the house. I refurbished an early 80s Fender 75; 2X6L6 - 75 pounds, that is, one pound per watt. Much too heavy with a tired EV 'Force' speaker (Force? May the Force be with you?).

My last Pro ... replacement Power Trannie and Rola replacement speakers ... I did a cap job and it sounded okay Then, put some exc. condition Jensen '65 C12-N speakers in it. It sounded absolutely incredible. That's generally the formula: caps and a fresh speaker. A little surprising it didn't perk up with the new OT.

So, I think speakers can make a big difference IF they are more efficient, giving you more dBs per output watt. Agree.

Having said that, I think D120s weigh around 16 pounds each. That's a lot of weight to be hanging off the thin, particle-board speaker baffle in a Thunderbird or a Thunder 1 RVT. Hmmn, maybe an efficient Neo speaker with a super-light magnet and correspondingly less frame weight would work in this application? Yes, that would work although I've had one disappointment with a 10" Jensen RI; don't know that much about their Neos but IIRC, they have a lot more power handling than necessary, no? Rated for 100 watts?

On a final note, I know there are several different variations of Thunderbird; 1x12 & 1x8, 2x12, etc. Is there one variety/generation/year that people prefer over another? I'm not sure these stayed in production long enough for one model to gain popularity over the others; one measure of how few were sold originally is the small number on eBay. Unfortunately, the cabinet construction may also have contributed to the small number of survivers.

If the Thunderbird were wired like the T1 with the reverb amp contributing to the 'dry' signal, I'd want a larger reverb speaker. Given that the Thunderbird's reverb amp only works when a 'wet' signal is wanted, having another 10" or 12" speaker adds alot of weight for 'part-time' use.

gilded

If I were as interested in a T-Bird as you; I'd think about contacting the guy. Other than John K's, there are very few T-Bird transactions at all and even fewer over $300 suggesting the seller is drinking the Kool Aide. He may also be fronting for the owner which means there's another $200 in vig in the deal. For all my making fun of him, fact is we don't get to pick our sellers and, chances are that with caps/tubes/a reverb can, the amp probably has a shot at being a winner; a better shot than the one w/ 2 - 8" speakers. Said another way, you might try offering him say $550 delivered - all he can say is no.

Regards, cj
 

gilded

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My last Pro ... replacement Power Trannie and Rola replacement speakers ... I did a cap job and it sounded okay Then, put some exc. condition Jensen '65 C12-N speakers in it. It sounded absolutely incredible. That's generally the formula: caps and a fresh speaker. A little surprising it didn't perk up with the new OT.

Actually, cap'n, I didn't change out the OT on this one. It already had a replacement PT (a bit more voltage than stock),
but the OT was orig.



Having said that, I think D120s weigh around 16 pounds each. That's a lot of weight to be hanging off the thin, particle-board speaker baffle in a Thunderbird or a Thunder 1 RVT. Hmmn, maybe an efficient Neo speaker with a super-light magnet and correspondingly less frame weight would work in this application? Yes, that would work although I've had one disappointment with a 10" Jensen RI; don't know that much about their Neos but IIRC, they have a lot more power handling than necessary, no? Rated for 100 watts?

The little I know about speaker ratings seems to revolve around the 'tuffness' of the voice coils. Some of the newer materials are
very good at absorbing the heat byproduct of high wattage but are still very light; they get a higher power rating, but don't slow down speaker movement with excess weight. An example would be, say, Celestion g-12m speaks from the '60's to the '70's. Oftentimes the same speaker cone, but the wattage changes from 25 watts up to 65 watts because the voice coils change from cardboard to some plastic-y stuff whose name I can't remember.
[/quote]


Anyway, I thank you so very much for all the good input on the T-birds and the T1s. I'm actually looking for a cleaner sound than most folks. I play a '53 ES 175D a lot, as well as a Strat, a Ricky 12 and a LP. None of them will cut through the drums and we're not playing that loud.

Also, the headroom issue is important. I friend jammed with my trio the other night, on a Gibbie 345. I loaned him a Vibrolux Reverb and played the T1 RVT with a Strat and the 175D. He loved the sound of the T1 (quite rightly) but there was no headroom left. Later, after the drummer left, we played with just piano, bass and drums. The T1 was almost perfect. I just need a little more oomph. I'm hoping a T'bird will oomph me.

I like what you are thinking about dropping an offer on the Covington, Ky. guy. I may just do that.

regards, gilded
 

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My '67 Thunderbird that I used to own definitley a different sound, not just a "bigger" version of my '67 Thunder 1 RVT. So just keep that in mind. A solid state rectifier w/7591 power section is not as "sweet" as a rectified EZ81 w/6GW8's. So yes you will get the "volume/headroom" w/Thunderbird but the sweetness of the T1 RVT may not be there. You're mileage may vary as they say. Plus, I don't think Fender single coil guitars are that well matched for Guilds as a humbucker or high output single coil (IMHO). My Tele sounded better through my T1 RVT and kind of well, bland through the Thunderbird. I think Thunderbirds are exceptional for Jazz or clean Ventures, instrumental surf style music.

I actually have a nice '69 Thunderstar Amp (1x12) that's better constructed and much more versatile than a Thundebird that I was looking to sell, if anyone is interested. It has a seperate power (7591s) and preamp chassis. The reverb is integrated like a Fender, not a seperate power amp (but uses a 6GW8 as the reverb driver!) and a 12DW7 for the phase inverter which really gives a nice rectifier feel. I need to sell it as I finally found a clean '62 Guild 99-J amp!!


So back on subject, I'd recommend to turn the the volume know down on the your drummer :) and get a heavier duty speaker and copper cap rectifier. This way you and your drummer can compromise, meet each other 1/2 way.

BTW - What a great forum! Glad to come aboard!
 

capnjuan

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gilded said:
Actually, cap'n, I didn't change out the OT on this one. It already had a replacement PT (a bit more voltage than stock),but the OT was orig. My new reading glasses are in the mail :oops: .

The little I know about speaker ratings seems to revolve around the 'tuffness' of the voice coils. Some of the newer materials are very good at absorbing the heat byproduct of high wattage but are still very light... Good point; it has to be in the material in the voice coil - otherwise there's no visual distinction between a 25W speaker and a 125W speaker.

Also, the headroom issue is important...I just need a little more oomph. I'm hoping a T'bird will oomph me. Dang; :evil: don't be talkin' that Ricky 12 talk around here, gonna make everybody (including me) green with GAS ; more on headroom below.

I like what you are thinking about dropping an offer on the Covington, Ky. guy. I may just do that. For over a year, a NY music store listed a T1 RVT on eBay in good cosmetic condition for $699; not for auction, just for sale - on/off/on/off until he put it up for auction and told a whopper about how Mike Bloomfield had played a T1 professionally. I asked the seller how he knew that to be true; no answer, he sold the amp at auction for $600; more than two times what good copies go for. The point is that for this guy's T-bird to move at a price near what he's asking, he's gonna have to come with something like: "...Jimmie Hendrix kept a T-Bird for practice...", otherwise it's going to sit there.
Gerald Weber's books address gain/headroom and he suggests increasing the voltage in the preamp. The pic below is the 1st 12AX7 preamp tube in the T1 RVT. The first (upper) half has a 150K plate resistor, the second half, used to operate the Tremolo, has a 220K plate resistor. If you are capable or know someone who is, you might want to consider dropping the the 1st stage. Unfortunately, there are no commonly available resistors between 100K and 150K but two 68K resistors in series would replace the 150K with 136K of resistance increasing the voltage on the plate.

Because the outcome is somewhat subjective, this is a trial and error process but, in any event, I wouldn't reduce that resistor to anything less than 100K total - however you arrive at a value. This necessarily means yanking the chassis over and over. Because the second half's plate resistor is tied to the bias, you ought not to mess with it.

T1preamp.jpg


I've done this with a Gibson GA5 and got a 'hotter' somewhat more 'driven' sound out it. In any event and short of replacing the power supply, I don't know of anything else that will effect the amp's gain. If this is too troublesome, you might consider JazzWest's suggest on the Weber rectifier; I think he's right that it will 'dry' the sound out some; maybe a little more articulate and the rectifier will still slow down the B+ allowing the filaments to heat up.

cj
 

capnjuan

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JazzWest said:
So just keep that in mind. A solid state rectifier w/7591 power section is not as "sweet" as a rectified EZ81 w/6GW8's...
So yes you will get the "volume/headroom" w/Thunderbird but the sweetness of the T1 RVT may not be there...I actually have a nice '69 Thunderstar Amp (1x12) ....that I was looking to sell, if anyone is interested. .... I need to sell it as I finally found a clean '62 Guild 99-J amp!!
Hi JazzWest: Thank you for your comments on the T1 v. the Thunderbird. I've never had the pleasure with a Thunderbird but I'd have to agree on the 'sweetness' thing; part of it must lie in the somewhat 'spongy' quality of tube recitifiers in general and the fact that the T1 was 'tilted' towards clean.

There's a thread here somewhere where Kap'n pointed out the importance of cathode caps in shaping bass response. The T1 uses a pretty large value cap in the first preamp 12AX7 - sorry that it isn't clear but it's 32uf/25V. By way of comparison, many Marshalls, with their reputation as 'screamers' use .68uf caps in that postion and the highly regarded 59 Bassman uses 50uf. As I understand it, a cap with that large a value will pass lower frequencies but impede higher ones including sonic 'hash' and 'grit'.

T1cathodecap.jpg


The T1 also has large value coupling caps; .15uf shown below as opposed to most amps of the period relying on values between .02 and .05; these large value caps have the same influence on frequency that cathode caps do; larger values mean reduced hf 'noise' which will promote a 'clean' signal. As I mentioned here before; I've pumped a Marshall Bluesbreaker II into a T1 and got 'clean' on the output; not a criticism, a comment on design.

T1couplingcaps.jpg


Why don't you post your Thunderstar in the BB's For Sale / For Trade Forum; I can think of several BB folks who might be interested and, as always, the more pics the better. Do you have a schematic? If so, would you consider emailing it to me? Thank you.

cj
 

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Posted a version of this the other day, but it didn't make through my old-time country server up in Ashcroft. I'll try to remember what I said.

My Thunderbird has 1x12" and 1x8" speakers, mounted in a particle-board baffle. The spring reverb is mounted in the chassis. I paid $276 plus shipping, plus about $80 for a new set of 12AX7s. Even got the original cover. As I remember the measurements, the speaker board is about 15" x 22" - nowhere near big enough for a 15" and 2x8" speakers.

Matsickma has informed us previously of a later Thunderbird model with 2x12" speakers - it might be that this would be big enough for a 15" and 2x8", and a Superbird with 2x15". Here's the story:Matsickma on Thunderbirds and Superbirds

Most important, I've just spent three days with a bunch of great musicians, 35 in all, at our place up-country. Some have lots of electric guitar/tube amp experience. They liked the Thunderbird a lot. Lots of headroom, linear pre-amp volume pots, they liked the reverb (I has been concerned, but I'm now assured that it sounds just fine) and tremolo. One friend, a confirmed Fender fan, said that it was a "tone monster" and he would put it up against any Fender Twin he knew. Others commented on the huge tone variations available with the slilde switches - they obviously control something more than simple cutoff filters - Cap'n, can you decipher from the schematics what else they do?

Played it side by side with a T1-12 - the T1-12 is very sweet, although I'm not too fond of the tremolo. But the Thunderbird just plain honks. I will swap out the no-name 12" for a broader-spectrum speaker, but overall I'm a very happy camper now.

Next step is to rebuild my other Thunderbird that dissolved in shipping. Now that I know what I'm aiming for, looks like good fun ahead.

Cheers, all, keep on Thundering
 

gilded

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A great story about your guests appreciating the T-bird.
FWIW, my friends like the T1 RVT, too, even the Marshall and Matchless guys.

Could any of you guys tell me how heavy a T-bird is? I don't really care, but my back wants to know.

gilded
 

gilded

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61 pounds???? 61 pounds???? With a medium weight 12" speaker and and an 8" CTS? Owwwh!!!
My 'back' wants me to buy two T1 RVTs, instead!

I'm beginning to see why they made 'em out of particle board.
I wonder how much a plywood cab version would weigh?

Come to think of it, how much does a Thunderstar weigh?
 

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Here's my '69 Guild Thunderstar amp (which I'd like to find a good home as I just do small gigs that my little Thunder I covers it) . Weight is the same as a Thunderbird, but ligther than a Fender Super Reverb yet similiar in dimensions. I sold my '67 Thunderbird and kept the Thunderstar it had a sweeter, compressed tone, like a Fender Vibrolux. Maybe the 12DW7 phase inverter used by the Thunderstar has to do with the sweetness? I do have a schematic for the Thunderstar that I purchased from Musicparts.com .

gstar_1_150x112.jpg


gstar_2_150x112.jpg
 

capnjuan

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john_kidder said:
they obviously control something more than simple cutoff filters - Cap'n, can you decipher from the schematics what else they do?
Hi John; I'll take a look but, as Matsickma pointed out, there are three versions of this amp in play; I have one schematic but it doesn't indicate which model - if separately ID'd - it applies to. Thanks also for the link to Matsickma's discussion.

Dang, now I want one! cj
 
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