Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bnwitt on October 09, 2017, 11:18:54 am
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So I'm now building my 4th Hoffman AB763 amplifier in as many months, and this one is the 4X10 Super Reverb version for a local player's Christmas present from his wire and grandmother. Great ladies for sure. I've just finished the circuit board and just have to clean it with pick and alcohol and it will be ready to install. Chassis will be here Wednesday and everything else has arrived. I just happen to have a raw BFSR cabinet in stock from many moons ago so today I will be tolexing and grill clothing it while awaiting the chassis.
The family members chose the 40 watt 4X10 version of the amp after the player played one of my Duke 65 amps (Hoffman BFDR) which I built for his father. This is the fellow who said the Duke 65 was the best amp he had ever played and who had been in lots of local L.A. studios playing their amps. So, I'm a little worried he won't get the same early breakup and magic tone he experienced with this more powerful version compared to the 1X12 22 watt version. I know the 40 watt SR version has the 0.022uf mid caps and the undersized 100Ω NFB resistor for the 2Ω OT (which is supposed to allow it to get dirty faster than if it had the proper 200Ω value) but I'm just not sure. I also know that lots of folks love the BFSR tone and I've built several 1X15 40 watt VV versions that are sweet but loud according to the players who own them so I'm hopeful it will work for him. This player uses a pedal board and has been playing a Fender Blues Deville for the last few years so I guess he is used to 40 watts. Do any of the players in here play an SR amp? If so, what do you think about it?
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I don't play one yet. But have had several in for recaps and 3 conductor power cords and really loved the beasts. Sweet cleans and lotsa balls. Liked them so much that I have an SR chassis sitting in the cradle right now. That populated board in the pic looks great and mine will be black. I see you used chicklet caps which I have found to sound pretty good. I've built the last 2 amps using them and I really can't tell a difference between them and pricier caps. (Could be my electronic ears though). Look at the AA763 which has .033 mid cap and 820 ohm fb resistor at 2 ohms OT. One could try different values on the mid cap and fb resistor to suit taste.
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... and the undersized 100Ω NFB resistor for the 2Ω OT (which is supposed to allow it to get dirty faster than if it had the proper 200Ω value) but I'm just not sure.
The various model AB763 amps use 100Ω or 47Ω NFB resistors. None use 200Ω resistors. The size of the resistor is determined by the speaker load impedance for the particular models. Any model that has an 8Ω speaker load will use a 47Ω resistor. Models that use a 2Ω or 4Ω speaker load will use a 100Ω NFB resistor.
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Are you guys calling the 100 ohm resistor to ground on the bottom half of the PI on the schematics the fb resistor? If so then what do we call the 820 ohm resistor coming off the 2 ohm tap of the OT?
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Any model that has an 8Ω speaker load will use a 47Ω resistor. Models that use a 2Ω or 4Ω speaker load will use a 100Ω NFB resistor.
Steve yes I know. However, the signal level from an 8Ω OT is different from a 4Ω OT and that is different from that of a 2Ω OT and technically speaking in order to maintain the same level of negative feedback signal keeping the series resistor at 820Ω one would expect the value for the shunt resistor to be:
8Ω=47Ω
4Ω=100Ω
2Ω=200Ω
I do realize Leo didn't follow that mathematical process on the 2Ω amps but it does change the amount of NFB on them. Right?
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Are you guys calling the 100 ohm resistor to ground on the bottom half of the PI on the schematics the fb resistor? If so then what do we call the 820 ohm resistor coming off the 2 ohm tap of the OT?
The 820Ω resistor is the series feed resistor. The 100Ω or 47Ω resistor is the shunt resistor. The ratio of these two resistors (in conjunction with the signal voltage level of the OT secondary) is what governs the amount of NFB sent to the PI
http://www.aikenamps.com/index.php/designing-for-global-negative-feedback (http://www.aikenamps.com/index.php/designing-for-global-negative-feedback)
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Thanks Barry, I was aware of that but wasn't aware you all called the shunt resistor the "feedback" resistor.
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I see you used chicklet caps which I have found to sound pretty good. I've built the last 2 amps using them and I really can't tell a difference between them and pricier caps.
Yes I've been using Xicon caps for most of my amps after going down the cork sniffer trail trying every different holy grail cap (original mustards, Mallory's etc etc) and coming to the same conclusion you have. It's all about value and quality of manufacture. I've still got quite a few PIO caps, original mustard caps, Mallory 150 caps but the Xicons are just fine.
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Thanks Barry, I was aware of that but wasn't aware you all called the shunt resistor the "feedback" resistor.
I probably should have been more specific. I see the two as integral and since the 820 doesn't really change across the different OT secondary designs, the shunt is the variable. That being said I do believe the 820Ω is the one more commonly referred to as the NFB resistor. With the 100Ω shunt on a 2Ω secondary the NFB signal level is lower at the PI so there is more distortion on those amps earlier on than the other amps.
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Where does one find a schematic of the Corona Amp Works Duke 65?
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Where does one find a schematic of the Corona Amp Works Duke 65?
It's nothing but a Hoffman AB763 2-channel so right here:
http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf (http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf) :laugh:
By the way, I love the look of a black Garolite circuit board. I've built quite a few amps with that color board. I've also used red, brown and the Marshall style hole grid brown. I think black is my favorite though. Right now I'm using up a green G10/FR4 4'x4' board and when I'm done with that I'll move on to the other colors I have in stock. Of course few will ever see them.
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Where does one find a schematic of the Corona Amp Works Duke 65?
Of course few will ever see them.
True but the black is really awesome to behold. It accentuates the colors of the components, they stand out against the black. Black is mysterious.... LOL
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What schematic did the 47 ohm feedback shunt resistor come from ?
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What schematic did the 47 ohm feedback shunt resistor come from ?
The deluxe reverb which has the 8Ω speaker load
http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Deluxe-Reverb-AB763-schematic.pdf)
You can also see it in any other 8Ω version like the Vibroverb with (1) 8Ω 15" speaker
http://el34world.com/charts/Schematics/files/fender/Fender_vibroverb_ab763_schem.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_vibroverb_ab763_schem.pdf)
The 4Ω versions of the amp have the 100Ω shunt resistor. Likewise the 2Ω versions which as I pointed out is not mathematically the same level of NFB. Theoretically, the 2Ω amps should have a 200Ω shunt. but, with 4 speakers driving the SPL I'm thinking less NFB allows more distortion sooner so that's probably a good thing.
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What schematic did the 47 ohm feedback shunt resistor come from ?
All AB763 amps that use an 8Ω speaker load will have a 47Ω resistor. That includes Deluxe, Deluxe Reverb, Vibroverb, and Showman (Maybe others, but those I have memorized). In fact, since the Showman was available as a single or dual showman, there's a note on the schematic for that resistor...
http://el34world.com/charts/Schematics/files/fender/Fender_Showman-AB763-schematic.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Showman-AB763-schematic.pdf)
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I see now. The last AB763 I assembled was a Hoffman single channel DR and the fb shunt in it is 100 ohm, and I guess it assumes an 8 ohm load. I never thought to try a 47 ohm there with 8 ohms. I also understand Barry's concern to get the right (best?) value based upon the impedance of the OT secondary. BTW that SCDR sounds really really nice.
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Black is mysterious.... LOL
black is over rated :icon_biggrin:
real artists use red (crimson alizarin) n blue (phalo) 5 to 10 layers should be good :icon_biggrin:
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I see now. The last AB763 I assembled was a Hoffman single channel DR and the fb shunt in it is 100 ohm, and I guess it assumes an 8 ohm load. I never thought to try a 47 ohm there with 8 ohms. I also understand Barry's concern to get the right (best?) value based upon the impedance of the OT secondary. BTW that SCDR sounds really really nice.
The first Hoffman DR I built this year went out with a 100 ohm shunt resistor and the owner loves the tone of the amp. That means a little more NFB is ok too I guess. Since I am not a big player, I am always seeking advice on the tone aspect of these amps from real players. I know some see these questions as nit picking, but I am passionate about player feedback. I'm not building these amps for me after all.
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i have a late 65 - early 66 BFSR. it is my favorite amp. right behind that is my 72 ampeg V4 played through a EV15L & EV12L in closed back cabinet. need to order a new cabinet and grill for the BFSR - it deserves a better home...
--pete
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i have a late 65 - early 66 BFSR. it is my favorite amp. right behind that is my 72 ampeg V4 played through a EV15L & EV12L in closed back cabinet. need to order a new cabinet and grill for the BFSR - it deserves a better home...
--pete
So Pete, The amp is not too loud for you? It seems everyone these days is going low wattage and shunning higher wattage amps.
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Alright, so doing the math on the NFB I get:
Deluxe 22 watts into 8 ohms V=sqrt(22*8) 13.3Vrms with 47Ω shunt
Vibroverb 40 watts into 8 ohms V=sqrt(40*8) 17.9Vrms with 47Ω shunt
Dual Showman 40 watts into 4 ohms V=sqrt(40*4) 12.7Vrms with 100Ω shunt
Super Reverb 40 watts into 2 ohms V=sqrt(40*2) 8.9Vrms with 100Ω shunt
Twin Reverb 85 watts into 4 ohms V=sqrt(80*8) 18.4Vrms with 100Ω shunt
So there are some discrepancies in the ratios between amps with similar voltage levels which I guess gives them slightly different tonal characteristics. The Twin's setup really explains why steel guitar players love it for clean.
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Hi..i am a new user here. In my case...
I have an SR chassis sitting in the cradle right now. That populated board in the pic looks great and mine will be black. I see you used chicklet caps which I have found to sound pretty good. I've built the last 2 amps using them and I really can't tell a difference between them and pricier caps.
turnkey pcb (https://www.7pcb.com/)
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Hi..i am a new user here. In my case I have an SR chassis sitting in the cradle right now. That populated board in the pic looks great and mine will be black. I see you used chicklet caps which I have found to sound pretty good. I've built the last 2 amps using them and I really can't tell a difference between them and pricier caps.
Good gravy - you copied part of my post word for word. See reply #1 above. :dontknow:
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First time poster. Probably clicked on quote by mistake and then didn't know what to do next. Give it another try Noell
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i have a late 65 - early 66 BFSR. it is my favorite amp. right behind that is my 72 ampeg V4 played through a EV15L & EV12L in closed back cabinet. need to order a new cabinet and grill for the BFSR - it deserves a better home...
--pete
So Pete, The amp is not too loud for you? It seems everyone these days is going low wattage and shunning higher wattage amps.
i am going deaf, so no. the ampeg v4 is just right. the BFSR is a bit lean on power... i don't push either amp into overdrive. i just like to dabble with surf style guitar and jazz. my hearing has rolled off completely at 6kHz and i can hear c8 on piano at about half volume of c4. i use an o-scope to check amp stability.
--pete
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i am going deaf.... my hearing has rolled off completely at 6kHz and i can hear c8 on piano at about half volume of c4. i use an o-scope to check amp stability.
--pete
Join the club brother! Notice the exclamation point for a fellow Hard of hearing tuber. I use my wife to verify OT reverse polarity squeal and other oscillations. Sometimes the dogs let me know too.
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i am going deaf,
--pete
Pete are you using hearing aids? I have since around '93 or so and it makes listening to certain pitches very difficult, so I can relate to both you and Barry's
conditions.
~Jim
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no hearing aids yet. i do need to get a pair.
--pete
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Whadja say, sonny?
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Whadja say, sonny?
I said is that a breadstick over your ear?
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> one would expect the value for the shunt resistor to be:
> 8Ω=47Ω
> 4Ω=100Ω
> 2Ω=200Ω
No--- in theory they should go by the Square Root of the nominal load. (You may have found this in a later computation.)
In practice: put in something close, smoke-test, pick speakers, then diddle this value (or the 820) more/less to taste. If you pick the 47/100 higher, the gain goes down and speaker damping increases. If you pick it low, gain goes up some and speaker is less damped. Happy damping depends a LOT on the speaker system (drivers and cabinet together), also the room genre and player.
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Well based on:
1. Leo Fender was smarter than me
2. The BFSR having phenomenal success to this day
3. CBS changes to the blackface amps being perceived by most as bad
I'm going with 100 ohms on the shunt resistor and leaving well enough alone. Thanks though PRR
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I'm going with 100 ohms on the shunt resistor and leaving well enough alone.
And so we've come full circle. :icon_biggrin:
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Actually even farther. When I started I didn't realize the journey was futile. :l2:
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Ok so I just received an SR chassis from Mojo yesterday and it is probably one of the worst chassis I've ever purchased. The flat unpolished oxidized galvanized finish was bad enough, but the vertical centerline for the control holes was off center and too high by 3/16". Also the bright switches were off horizontally and in fact every single hole was off from it's proper horizontal spacing (7/8" or 1-1/4") so by the last hole on the far right it was way off. I know Mojo is good about making things right so I've emailed them about a return. It has been a while since I purchased a chassis from them as I've been getting them from the fellow in Arkansas who's quality is pretty good but he was on vacation when I needed this one. He's back now so I ordered one from him this morning. The quality control on this was disappointing. You can see in the attached photo that the bright switch top mounting hole is on the top edge of the chassis due to the vertical center line error. The center line should be 15/16" from the bottom of the chassis and this one was centered at 1-5/64" Very bad.
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...the vertical centerline for the control holes was off center and too high by 3/16". Also the bright switches were off horizontally and in fact every single hole was off from it's proper horizontal spacing (7/8" or 1-1/4") so by the last hole on the far right it was way off. ...
I think there is supposed to be some vertical offset due to the control panel lettering being underneath the pots on the face plate. See 67 and 73 SR side by side for comparison (I had these in for maintenance a couple of months back)
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Another shot showing the 67 faceplate a bit better
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Yet another closer shot showing vertical offset (especially noticeable between top and bottom of the bright switches). (Note that this amp has had some of the original parts changed, including installing a 230V 50Hz PT)
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Bello ! :thumbsup:
Franco
p.s.: If you apply the anti rust bath, can you show us a bit the process with some photo ? I would like to see the aspect of the chassis immediately after you extract it from the acid bath (Thanks)
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Yes there is offset but not as much as this chassis had. The centerline on a typical blackface chassis should be around 1" to 1-1/16" from the bottom of the chassis measured at the face angle. This one was almost 1-1/4" from the bottom. The top screw for the bright switches was in the lip and the pot terminals were touching the underside of the top lip.
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Bello ! :thumbsup:
Franco
p.s.: If you apply the anti rust bath, can you show us a bit the process with some photo ? I would like to see the aspect of the chassis immediately after you extract it from the acid bath (Thanks)
Franco,
It's pretty simple. Mix Oxalic acid powder in hot water and soak the rusted metal overnight. Rinse and repeat if necessary. I'll post the after pic tomorrow.
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I see you used chicklet caps which I have found to sound pretty good. I've built the last 2 amps using them and I really can't tell a difference between them and pricier caps.
Yes I've been using Xicon caps for most of my amps after going down the cork sniffer trail trying every different holy grail cap (original mustards, Mallory's etc etc) and coming to the same conclusion you have. It's all about value and quality of manufacture. I've still got quite a few PIO caps, original mustard caps, Mallory 150 caps but the Xicons are just fine.
Im glad I read this now... I just orderd about 100 orange drops for a couple 5e3 builds. I already have a bucket full of xicon chiclets sitting around haha. :BangHead:
Also, your board looks great.
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Im glad I read this now... I just orderd about 100 orange drops for a couple 5e3 builds. I already have a bucket full of xicon chiclets sitting around haha. :BangHead:
Also, your board looks great.
It looks better now that it has been cleaned. :icon_biggrin: Have fun building your 5E3's. I love that amp circuit.
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So just a bit more on the Mojo Chassis saga. I have been issued an RMA but so far no prepaid shipping label. Hopefully that is just and oversight. We'll see. The Mojo guys seem like pretty nice fellows but I'm getting the feeling that they believe I'm some knucklehead who doesn't understand how Fender chassis are laid out. And in their defense, they are taking the chassis back (with return shipping paid by them I think) while possibly believing I'm a moron. :laugh: I'm sure they get that a lot but I have serviced, built and otherwise had my hands on a virtual plethora of Fender Tweed, brown, black and silver face amplifiers in the last 25 years. Literally hundreds of them. I have built at least 30 blackface clones and drafted and had engraved the custom faceplate for everyone of those amps.
Many of the blackface amps I've built were built in original Fender chassis which came my way one way or another without their original circuitry. Suffice it to say, I know pretty well how Fender chassis are supposed to be dimensioned. As I said in a previous post, the typical blackface Fender chassis has it's control holes centered at anywhere from 15/16" to 1" from the bottom of the chassis measuring along the angled face. The fellow in Arkansas, from whom I have been buying my chassis as of late, tells me he uses Mojo's dimensions for his replicas. I have also had good luck with Mojo's chassis in the past so this is obviously an anomaly. I don't know if someone was hung-over the day this chassis was made or out on a smoke break when the milling machine went off kilter but 1/8" up makes a huge difference when lining up knobs and lettering on a faceplate. Attached are a photo of both the 1967 Showman chassis I just cleaned up and the Mojo chassis I also had to buff out with a ruler clamped along the face. You will see the original Fender holes are at 1" exactly from the chassis bottom and the Mojo is at 1-1/8" That doesn't seem like much but it is. :dontknow:
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The fellow in Arkansas, from whom I have been buying my chassis as of late, tells me he uses Mojo's dimensions for his replicas.
I get my chassis from the same guys. Great prices and crazy fast shipping. And they have really beefed up their selection.
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I got my SR chassis from the Arkansas guys and the hole centerline in about 1 1/6" from the bottom.
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So just a bit more on the Mojo Chassis saga. I have been issued an RMA but so far no prepaid shipping label. Hopefully that is just and oversight. We'll see. The Mojo guys seem like pretty nice fellows but I'm getting the feeling that they believe I'm some knucklehead who doesn't understand how Fender chassis are laid out. And in their defense, they are taking the chassis back (with return shipping paid by them I think) while possibly believing I'm a moron. :laugh: I'm sure they get that a lot but I have serviced, built and otherwise had my hands on a virtual plethora of Fender Tweed, brown, black and silver face amplifiers in the last 25 years. Literally hundreds of them. I have built at least 30 blackface clones and drafted and had engraved the custom faceplate for everyone of those amps.
Many of the blackface amps I've built were built in original Fender chassis which came my way one way or another without their original circuitry. Suffice it to say, I know pretty well how Fender chassis are supposed to be dimensioned. As I said in a previous post, the typical blackface Fender chassis has it's control holes centered at anywhere from 15/16" to 1" from the bottom of the chassis measuring along the angled face. The fellow in Arkansas, from whom I have been buying my chassis as of late, tells me he uses Mojo's dimensions for his replicas. I have also had good luck with Mojo's chassis in the past so this is obviously an anomaly. I don't know if someone was hung-over the day this chassis was made or out on a smoke break when the milling machine went off kilter but 1/8" up makes a huge difference when lining up knobs and lettering on a faceplate. Attached are a photo of both the 1967 Showman chassis I just cleaned up and the Mojo chassis I also had to buff out with a ruler clamped along the face. You will see the original Fender holes are at 1" exactly from the chassis bottom and the Mojo is at 1-1/8" That doesn't seem like much but it is. :dontknow:
put a face-plate on the "bad" chassis and take photos - send them (mojo) those photos.
--pete
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put a face-plate on the "bad" chassis and take photos - send them (mojo) those photos.
--pete
I did that. That's how I got the RMA
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I got my SR chassis from the Arkansas guys and the hole centerline in about 1 1/6" from the bottom.
That's ok. Pushing it but that works
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Well anyone giving up the name of the Arkansas guys so we can get chassis to.
Bill
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Barry will respond I'm sure, but I am sure the guy is on E bay. Search for Deluxe Chassis's and it comes up.
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http://www.ebay.com/itm/Super-Reverb-style-Amp-Chassis-Blackface-Silverface-RI-/322670738653?hash=item4b20acbcdd:g:uSUAAOSwDuJWuTv~ (http://www.ebay.com/itm/Super-Reverb-style-Amp-Chassis-Blackface-Silverface-RI-/322670738653?hash=item4b20acbcdd:g:uSUAAOSwDuJWuTv~)
https://www.ebay.com/sch/zachmdhunter/m.html?item=322670738653&hash=item4b20acbcdd%3Ag%3AuSUAAOSwDuJWuTv~&rt=nc&_trksid=p2047675.l2562 (https://www.ebay.com/sch/zachmdhunter/m.html?item=322670738653&hash=item4b20acbcdd%3Ag%3AuSUAAOSwDuJWuTv~&rt=nc&_trksid=p2047675.l2562)
--pete
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Well anyone giving up the name of the Arkansas guys so we can get chassis to.
Bill
Here is a link to their ebay page
https://www.ebay.com/sch/zachmdhunter/m.html?_nkw=&_armrs=1&_ipg=&_from= (https://www.ebay.com/sch/zachmdhunter/m.html?_nkw=&_armrs=1&_ipg=&_from=)
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Well I finally got my chassis and am back on track building this Hoffman 4X10 AB763/6G16 amplifier. Unfortunately (or fortunately if one thinks about the mortgage) I'm buried alive in solar work again. I managed to get the cabinet finished while I was waiting on the chassis but I probably won't get the chassis finished until next weekend.
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Well I finally got the face and rear plates yesterday so now I can finish the chassis. The only thing left on the cabinet is installing the tilt legs and top back panel which needs tolex but I ran out of glue. Like Rosanne Rosanadana says, "If it's not one thing it's another.
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I love 6G16s. My ideal amp. A crossover between a BF Reverb amp but with nicer bias-vary trem on the output tubes. Kind of like an upscaled BFPR, but with 2 channels, an LTP, 6L6s and more speakers. :)
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I do believe this is going to be an awesome gigging amplifier. This is the first 4x10 version of Doug's AB763/6G16 amp I've built though I have built several 1x15 V V 6L6 versions and they sounded fantastic. Way too loud for me but this customer is used to the 40 watt 4x10 amp type so he should love it. And this is his Christmas gift from his wife and grandmother! Lucky dog for sure.
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Always been my go to amp, & yours looks like it's coming on superbly (no pun/maybe little intended) but are those c10s....new Jensen's? I didn't like em unless only one in the mix. 1 out of 4.
I liked mix of cheaper webers, alnico, & ceramic. A while back a guy posted his build of SR with speaker auditions (think all Weber) & I seem to remember liking 4 different speakers best.
Think they add to richness, complexity....sorta like chorus of different voices. Long as one of em doesn't have laryngitis.
But what do I know....I like my Bantam Bass with stock 18" rectangle/parallelogram whatsit.
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Well there is more than one C10. These are C10Qs which I have used before and I like them. Hopefully the new owner will too.
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Looks like it is coming along nicely. My personal all time favorite amp, but these days I only use them for outside gigs. You notice I said them. :laugh:
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Well solar has been keeping me buried for the last few weeks but this holiday weekend I will be finishing the Hoffman AB763/6G16 4X10 amplifier. Then it goes to the father of the new owner for a burn in period where any rattles or other issues can be identified by his ears which are better than mine. I'll post some pictures of the amp when it is done.
And then I get to build the Hoffman Princeton Reverb 1X12 and the Sluckey AC15 1X12 for my studio for which I've been collecting parts. I can't wait to add these two amps to the stable. I'm using Doug's very nice computer drilled turret boards for both of these amps. It sure makes things a lot easier.
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Looks like it is coming along nicely. My personal all time favorite amp, but these days I only use them for outside gigs. You notice I said them. :laugh:
I missed this comment. How many BFSR amps do you have Ed?
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Barry - what is the length of the spacers under the turret board. I was suprised to see only 4 points to mount the board, but then again the board is pretty rigid.
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I am using 3/4" stand offs if that is what you are asking. 1/2" would be fine as well. Yes the 1/8" G10/FR4 board is very rigid. With the horizontal spacing between the stand offs at around 12" and the max overhang of about 2 1/4" on the power end of the board there is zero flex in the board on either end or in the middle. Being the overkill kind of guy I am, I would use (6) supports (even though (4) is enough) but it is really difficult to find places to put them with all of the transformers, cap cans etc, etc on the back side of the chassis.
Oh and by the way, for those of you watching this build, I was working on the final wiring yesterday and found a missing component on the board. The 0.1uf 250V coupling cap from the preamp to the phase inverter pin 7 had not been installed. Now I went over the board multiple times and didn't see that and this just goes to show that to err is human. You can see the added pink-ish 630 volt version I put on the board in the new attached picture which isn't present in the photo in my earlier post.
I've built so many of these amps now that one would think I wouldn't miss such a thing, but I did. So Doug's number one rule of amp building "if everything were correct it would be working." always applies. This is why taking your time and double/triple checking every component value and connection against a good layout drawing as you go along is essential to a trouble free start up. Now that I am twisting wires I am even ohming each lead from one end to the other to make sure the proper control wire lands on the proper board component. I'll be finishing the heater wires this morning and before start up I will once again check every component value and every connection against the layout to make sure all is correct. Then a voltage check before tubes go in. Check, check, check, check and check. :think1: And one more thing, yes there are two wasted 100 ohm heater artificial center tap resistors on the board. This PT had a heater CT.
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Thanks Barry.