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05-20-2010, 04:46 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | | Changeing the stock the required resistance (ohm) of a tube amp
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Hello fellow bass nerds. Does anyone know if it is possible to change the required resistance of a vintage tube amp? I know it's a long shot and that fiddeling with your beloved amp is a bad idea - in most cases.
Does any of you have experience with such a procedure?
Peace!
Jeppe
Copenhagen
Oh and sorry for the error in the post name. Im unable to edit it... bummer. |
05-20-2010, 05:15 AM
| | Registered User
Endorsing: Ampeg | | Join Date: Apr 2005 Location: Apopka, FL | | | you're right...bad idea. you'd have to re-engineer the whole thing.
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05-20-2010, 05:28 AM
| | Registered User | | Join Date: Jul 2009 Location: Bristol, UK | | | If you don't know the difference between resistance and impedance, probably shouldn't consider doing it yourself.
I'm guessing you mean the output impedance requirement. Generally that would be an output transformer change, and depending on what amp, probably need to get one made to suit. Pretty major task.
Much easier to change the impedance of cabs. |
05-20-2010, 05:31 AM
| | Registered User
pedal / amps - MAMMOTHsound | | Join Date: Apr 2009 Location: sheffield, uk | | Quote:
Originally Posted by Jeppe Madsen  Hello fellow bass nerds. Does anyone know if it is possible to change the required resistance of a vintage tube amp? I know it's a long shot and that fiddeling with your beloved amp is a bad idea - in most cases.
Does any of you have experience with such a procedure?
Peace!
Jeppe
Copenhagen
Oh and sorry for the error in the post name. Im unable to edit it... bummer. | can either get the transformer rewound or if its just a case of the output taps being 5.3ohms and stuff like that just use a speaker thats fairly near the standard rating.
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riffriff.
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05-20-2010, 08:39 AM
|  | Hey, what does this knob do? | | Join Date: Sep 2008 Location: New Hampshire | | | Be more specific around amp and cabs. Some amps play games with the speaker jacks and winding switching. You may be able to re-engineer that circuitry fairly simply. |
05-20-2010, 09:36 AM
|  | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by Jeppe Madsen Hello fellow bass nerds. Does anyone know if it is possible to change the required resistance of a vintage tube amp? I know it's a long shot and that fiddeling with your beloved amp is a bad idea - in most cases.
Does any of you have experience with such a procedure? | Yes. Please fill in your profile so that we may know which specific amp you are inquiring about.  |
05-20-2010, 02:53 PM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | Quote:
Originally Posted by Mr. Foxen If you don't know the difference between resistance and impedance, probably shouldn't consider doing it yourself.
I'm guessing you mean the output impedance requirement. Generally that would be an output transformer change, and depending on what amp, probably need to get one made to suit. Pretty major task.
Much easier to change the impedance of cabs. | Ha ha... Touché. |
05-20-2010, 02:59 PM
|  | Registered User | | Join Date: Feb 2005 Location: Seweracuse, NY | | Quote:
Originally Posted by Passinwind Yes. Please fill in your profile so that we may know which specific amp you are inquiring about. | Well, at least you know he's male.
__________________ fEARful: for those who want something better: http://greenboy.us/fEARful/ For Sale (locally only): Bergantino HT115 with Cover: $500.00. PM me about it.
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05-21-2010, 01:15 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | Quote:
Originally Posted by BurningSkies Well, at least you know he's male. | Hey...
Filled in my profile... Well i was thinking of changeing the impedence of my Hiwatt lead 100 amp. Its running in 8 or 16 and i need it to run i 4 ohm.
I know it isn't possible... |
05-21-2010, 01:29 AM
|  | Registered User
Head Tinkerer, The Flufflab | | Join Date: Mar 2009 Location: California | | | It should be possible to chain another transformer with a 2:1 ratio after the OT. That way you wouldn't have to tinker with the amp internals at all.
I'd experiment with something less valuable first though.
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05-21-2010, 08:38 AM
| | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by Jeppe Madsen Hey...
Filled in my profile... Well i was thinking of changeing the impedence of my Hiwatt lead 100 amp. Its running in 8 or 16 and i need it to run i 4 ohm.
I know it isn't possible... | What model number Hiwatt is that exactly, please? Every schematic I found for 100 watt Hiwatts clearly shows a 4 ohm tap on the output transformer. |
05-21-2010, 09:15 AM
|  | Registered User | | Join Date: Aug 2007 Location: Toronto Ontario Canada | | Quote:
Originally Posted by Passinwind What model number Hiwatt is that exactly, please? Every schematic I found for 100 watt Hiwatts clearly shows a 4 ohm tap on the output transformer. | Agreed, I've yet to see a Hiwatt without 4,8 and 16Ω taps. Perhaps the selector switch has been changed.
Paul |
05-22-2010, 03:51 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | Quote:
Originally Posted by BassmanPaul Agreed, I've yet to see a Hiwatt without 4,8 and 16Ω taps. Perhaps the selector switch has been changed.
Paul | Hey thanks a lot for the replys. It's actually a 1980s Hiwatt build for guitar - works okay for bass. I haven't been able to find much info about it on the interwebs. The impedence selector only has 8 or 16 ohms. It has a overdrive stage - thus the name Lead 100 i guess. I read some where that they where only made in a limited run. It was propably build during the later Hiwatt period - where the not so attractive amps where produced. It sounds great though in my opinion.
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05-22-2010, 05:55 AM
| | Registered User
pedal / amps - MAMMOTHsound | | Join Date: Apr 2009 Location: sheffield, uk | | | yeah definatly a later model, any reason you have to have a 4ohm load? Valve amps don't put out more power into lower impedence
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05-22-2010, 06:06 AM
| | Registered User | | Join Date: Feb 2005 Location: Edinburgh & Dundee, Scotland | | | Is it because you want to use your 4 ohm ampeg cab with it?
The easiest thing to do would be to rewire your speaker cabinet. Take the crossover out of the circuit, and, as it's a 4 ohm cabinet, I'm betting it uses 4x 4ohm speakers, wired in series/parallel. If that is the case, you could put all the speakers in series, giving you a 16 ohm cab.
Set the amp to 16 ohms. Good to go.
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05-22-2010, 06:34 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | Quote:
Originally Posted by i_got_a_mohawk Is it because you want to use your 4 ohm ampeg cab with it?
The easiest thing to do would be to rewire your speaker cabinet. Take the crossover out of the circuit, and, as it's a 4 ohm cabinet, I'm betting it uses 4x 4ohm speakers, wired in series/parallel. If that is the case, you could put all the speakers in series, giving you a 16 ohm cab.
Set the amp to 16 ohms. Good to go. | Hey Mohawk. I'll consider that. And yes you are right. I want to use it with my ampeg svt 410 hlf.
Daern it, I should have bought B410 HLF it runs in 8 ohms i believe...
Thanks! |
05-22-2010, 06:36 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | | I will have to use my Musicman HD 130 for now... |
05-22-2010, 09:49 AM
| | Registered User | | Join Date: Aug 2007 Location: Toronto Ontario Canada | | | Take your amp to a tech and get him/her to check if the OPT has unused secondary taps. It could be that Hiwatt used a standard transformer but only wired the 8 & 16Ω taps.
Paul |
05-23-2010, 03:28 AM
| | Registered User | | Join Date: May 2009 Location: Copenhagen | | Quote:
Originally Posted by BassmanPaul Take your amp to a tech and get him/her to check if the OPT has unused secondary taps. It could be that Hiwatt used a standard transformer but only wired the 8 & 16Ω taps.
Paul | Hey that might be a good idea... I'm takeing my Musicman to a tech soon.
But I actually have my eyes set for a Hiwatt dr 103, 100 watts. I hope the seller is in for an amp switherooo. But I really don't think so.
The dr 103 runs in 4 ohms. How are those with bass? Any experiences with it as a bass amp? |
05-23-2010, 12:00 PM
| | Registered User | | Join Date: Aug 2007 Location: Toronto Ontario Canada | | | None with that particular amp but I do own a DR201 from '73. That has 4, 8,16 and 70V taps.
Most tube amps work well for bass so I don't foresee a problem there.
Paul | | Thread Tools | Search this Thread | | | | 
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