Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on March 02, 2011, 11:08:05 am
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Hi folks
I am just wondering if anyone has built Tubenits ac30 non trem with reverb?
This amp totally fits my bill - I would absolutely love to build this fella.
One thing Does anyone know what changes would be made to cut down on 2 output tubes?
ALso if ya have any recommendations for the correct irons (wit 2 output tubes) i'd really appreciate it.
Chassis and HEad Cab will be a recycled old amp for now - i reckon i can just stretch to the price rest of the parts for now.
I wonder does doug stock absolutely everything ya need for this build?
Anyways thinking out loud!
thanks again folks
(http://music-electronics-forum.com/attachments/6372d1253625347-ac30-reverb-layout-draft.gif)
(http://music-electronics-forum.com/attachments/6371d1253625336-ac-30-reverb-draft.gif)
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I have not built that amp either. It's a draft idea. However, I have implemented reverb in that fashion prior to an LTPI numerous times and like the sound of it.
You can also look in Hoffman's Library of Information and see his AC-30 layout and also look at his "add reverb to a Western circuit" which he states he has used successfully on AC30 amps.
Look at Doug's 18watte PT and OT. The component values are probably all carried by Hoffman. Just look at his parts store.
With respect, Tubenit
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Thanks Dude
I stumbled across that through a google search - hope you dont mind me digging it up.
I appreciate the emphasis on having NOT built it!
Theoretically though it 'should' work right ? :)
I just Printed the Hoffman layout and your schem - poured a cup of tea and lit the fire - gonna go over them now :)
This amp would literally be exactly what i was looking for a couple of days ago here.
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Thanks Dude
I stumbled across that through a google search - hope you dont mind me digging it up.
I appreciate the emphasis on having NOT built it!
Theoretically though it 'should' work right ? :)
I just Printed the Hoffman layout and your schem - poured a cup of tea and lit the fire - gonna go over them now :)
This amp would literally be exactly what i was looking for a couple of days ago here.
I've built 2 AC30's both w/o trem + verb.
One à la JMI -tags boards- , the other à la Hoffman -glass epoxy turrets board-. Therefore, I won't be able to talk about the Reverb section.
Yet, both amps works perfectly well, & I must shout that the .1 cathode bypass cap on V1 (either on the TB or the Normal section ) is a real improvement to the tone of the amp. It indeed sounds less muddy.
Concerning the parts, you should get everything @ Doug's store. :wink:
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I could be wrong, but the only changes I can think of with 2 tubes instead of 4 would be:
- double value of power tube cathode resistor
- halve value of power tube cathode bypass cap
- double primary impedance of output transformer
- cut current rating of power transformer almost in half (preamp stays constant but 12AX7s don't draw much except for heater current)
- reduce current rating of choke by two (2) EL-84 screen grids (not really necessary but might be cheaper)
PT and OT for AC15, Matchless Lightning, Marshall 18 Watt all ought to work OK provided they have enough heater current for your circuit.
tubenit, et al will correct me where I'm wrong (hopefully)
Chip
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you guys are absolute legends.
Thanks so much for the feedback - I mean to get on with this now.
If the 18watt transformers are up to the job i know doug sells em so i'd be in business.
Gonna do up a parts list in the morning.
Might have a choke and reverb transformer / tank question but i'll do a bit of reading first.
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Use Doug's reverb trannie and tank for the one tube reverb. Typical to what you'd see on a Princeton Reverb, or DR.
Your other option is a passive effects loop with a Boss digital delay in it. May be easier for you to do & sounds pretty good, IMO.
With respect, Tubenit
Here is another option to consider that would have somewhat of a Vox tone, I think. It has a paralleled V1, Post Phase Invertor Master Volume, and a passive effects loop. It also has a lower value cathode cap on V1 and on the power tubes. And it has lower value coupling caps after the LTPI.
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If the 18watt transformers are up to the job
They are....... :smiley:
G
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thanks again - i think i may stick with the reverb version.
I am thinking the choke should be 8H 120ma going by ac15 specs...
is there a spec sheet available on the heyboer 18watt transformers?
I think the next thing i'd like to do before buying all the parts is draw the layout based on the version below so i have a better understanding of the circuit and how it will all come together.
(http://www.el34world.com/Forum/index.php?action=dlattach;topic=11163.0;attach=22128;image)
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draw the layout based on the version below so i have a better understanding of the circuit and how it will all come together.
Did you see this thread?
http://www.el34world.com/Forum/index.php?topic=575.0
With respect, Tubenit
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cheers i did
but the youtube links at the end kinda scared me - sounded quite crunchy to me
i got a fantastic clean sound of the last ac30 i played which has made me crave the sound!
hopefuly its the way he was playing or volume.
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I was referring to the SCH schematic and layout.
I think the next thing i'd like to do before buying all the parts is draw the layout
I presume you noticed that the U-toob clips were of a EF86 vox style amp. That's a whole different tube then the 12AX7.
With respect, Tubenit