Members SciHi Posted November 3, 2009 Members Share Posted November 3, 2009 Originally Posted by gnolivos Has anyone driven 2x12" speakers with this amp? I'm building a head and cabinet for it... wondering if this is a stupid idea. 2 - 12's driven by a 5 watt tube amp is great! I like to mix the speakers. To keep to 8 ohms, I use 2 16 ohm speakers in parallel. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 3, 2009 Author Members Share Posted November 3, 2009 Originally Posted by gnolivos Has anyone driven 2x12" speakers with this amp? I'm building a head and cabinet for it... wondering if this is a stupid idea. Sounds HUGE through my Genz-Benz G-Flex 212 @ 4 ohms! Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 5, 2009 Members Share Posted November 5, 2009 Awesome... I'm debating what speakers to use, been wanting Celestion Greenbacks, but may try cheaper alternatives/clones such as WGS brand.I have decided to get 2x12" at 8 ohm each. This way I can use one speaker @ 8 ohm (which from this thread I understand the V8 can handle), or I can run them both in parallel at 4 ohm (which I *know* the V8 can handle).I plan to put a switch on the cabinet to drive one speaker, the other speaker, or both. I may have 2 different types of speakers in there, so this way I can experiment with the voicing combos... [anyone know what wiring diagram + switch would work?]Little worried about switching from 4 ohm to 8 ohm loads though... am I going to mess up my amp head with this?!I will post pics here of the completed head/cabinet in a bout 2-3 weeks. It will look like a mini-JTM45 Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 5, 2009 Author Members Share Posted November 5, 2009 I look forward to it gnolivos. Are you doing the carpentry yourself? Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 5, 2009 Author Members Share Posted November 5, 2009 Originally Posted by gnolivos I plan to put a switch on the cabinet to drive one speaker, the other speaker, or both. I may have 2 different types of speakers in there, so this way I can experiment with the voicing combos... [anyone know what wiring diagram + switch would work?] I believe Mojotone.com sells connector plates for cabinets that are prewired for stuff like that. Originally Posted by gnolivos Little worried about switching from 4 ohm to 8 ohm loads though... am I going to mess up my amp head with this?! Nope. I do it all the time with no issues. Trick is to be quick about it. Link to comment Share on other sites More sharing options...
Members Preacher Posted November 9, 2009 Members Share Posted November 9, 2009 Boy am I glad I came back to this thread. Thanks for the continued input, Verne! Originally Posted by Verne Andru I did manage to snag another V8 and have run it in stereo with the other one. Sounds great! Congratulations on picking up another! I was on the lookout for ya but didn't see too many MIAs... Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 9, 2009 Members Share Posted November 9, 2009 Ended up buying a 12" Celestion greenback, and a 12" Celestion G12H, will have both inside one 2x12 cabinet, and the Palomino driving them as a 'head'.I resolved to making the speaker cab stereo/mono capable. The wiring requires two Mono 1/4" jacks coming out of the speaker cabinet, and a DPDT switch that lets you switch between 2x12" in parallel to one jack (4 ohm), or two independent 1x12" channels, one to each jack (8 ohm each).This way, I can use a Mono configuration to drive both speakers together, or I can switch to Stereo configuration and split it up, to drive each speaker independently per jack (in which case I would connect the head to the specific L or R channel depending on which speaker I want to use... Diagram: (source: LINK)Verne: I still think that switching from Stereo to Mono (i.e., from 4ohm to 8 ohm) via a switch while the amp is ON is *not* a safe thing to do. Comments? Originally Posted by Verne Andru Nope. I do it all the time with no issues. Trick is to be quick about it. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 9, 2009 Author Members Share Posted November 9, 2009 Originally Posted by Preacher Boy am I glad I came back to this thread. Thanks for the continued input, Verne! Congratulations on picking up another! I was on the lookout for ya but didn't see too many MIAs... I appreciate the thought and thanks. There don't seem to be many of these around anymore - either on eBay or CL. Frankly if they made 500 total I'd be surprised. I tried a couple sellers on CL and finally found one who would ship, but only after there was no interest from his local community. It's mint and I got it for $100 plus $35 shipping. The second one does sound much better than how my first sounded before the mods so there does appear to be some variance from one to the next. Originally Posted by gnolivos Verne: I still think that switching from Stereo to Mono (i.e., from 4ohm to 8 ohm) via a switch while the amp is ON is *not* a safe thing to do. Comments? It comes down to understanding what's going on in the circuit. The output section runs through an output transformer so what goes to the speaker is somewhat isolated from what's going on inside the amp. The danger comes in putting an incorrect load on the transformer for a period of time. In most cases this will cause the transformer to overheat which usually causes the transformer windings to melt and short before any damage happens to the circuitry driving it. As long as you're just changing things by flipping a switch I don't see how you can cause any damage - unless the switch shorts. But if you are nervous, simply turn the amp off, make your change and turn the amp back on again. Bear in mind it gets pretty hard on the tube since you are causing them to heat/cool/heat.Question: Has anybody done any of these mods? Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 10, 2009 Members Share Posted November 10, 2009 Which mods specifically? Originally Posted by Verne Andru Question: Has anybody done any of these mods? Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 10, 2009 Author Members Share Posted November 10, 2009 Any of them? I guess what I'm asking is -> is it worth my time to work up a consolidated schematic with all the mods. If no one's doing them, then it's not really an issue. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 10, 2009 Members Share Posted November 10, 2009 I'm certainly WANTING to do the mods. I think if you could find the time to consolidate them in one 'post' that would be awesome. I think I have a good idea of what to do, but it took a good while to read through! Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 15, 2009 Members Share Posted November 15, 2009 Here's a little teaser for you guys... progress on the 'mini plexi' cabinet I am building with V8 guts. I am also having a 2x12 cabinet built, with Celestion speakers.And the speaker output on the back: Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 16, 2009 Author Members Share Posted November 16, 2009 ^^ Looking good. Link to comment Share on other sites More sharing options...
Members Preacher Posted November 16, 2009 Members Share Posted November 16, 2009 Yeah, I would dig the schematic for sure. I think I got the basic idea of what you did but so far I've just done the C12 & C9 lift. But thanks for all the work you've put into it documenting this far. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 19, 2009 Members Share Posted November 19, 2009 Verne, Would you be able to provide us with correct procedure to drain the capacitors in this amp? I already have built a wire with 10Kohm @ 5W ceramic resistor. One side needs to be clamped to ground (chassis), but for THIS AMP, what is the recommended point to drain the caps? You cannot really reach under the caps on the V8 without removing the board, so I am trying to find a good spot that you can reach on the TOP of the circuit, to tap into. Some people seem to even prefer downstream after the resistors etc.... What do you recommend? Link to comment Share on other sites More sharing options...
Members ContentSpooling Posted November 19, 2009 Members Share Posted November 19, 2009 Nice one. It's looking good dude. Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 19, 2009 Author Members Share Posted November 19, 2009 Pin 1 on V1 to ground, no resistor. This board holds a fairly serious charge, so be sure to test with a meter to make sure it's dead before you start mucking. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 19, 2009 Members Share Posted November 19, 2009 Pin 1 on V1 to ground, no resistor. I'm going to assume V1 is one of the tube sockets... at Pin #1. But which tube?Also, do you normally remove the tube to get to PIN1, or do you make contact at the base of the socket on the other side... I think you can access them through there, not 100% sure.And yes, I did look at the schematic! Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 19, 2009 Author Members Share Posted November 19, 2009 Originally Posted by gnolivos I'm going to assume V1 is one of the tube sockets... at Pin #1. But which tube?Also, do you normally remove the tube to get to PIN1, or do you make contact at the base of the socket on the other side... I think you can access them through there, not 100% sure.And yes, I did look at the schematic! I hope you don't take me for a jerk for what I'm about to post, but it needs to be said, so bear with me.This is one of the main reasons why it's difficult discussing this stuff on an internet forum. Particularly with the V8, we're dealing with dangerous voltage levels that need to be treated extremely seriously.What I posted above makes perfect sense to anybody who has a rudimentary understanding of what they are doing. Your question indicates this does not include you. No disrespect meant.At this point I would ask you to find a tech in your area who can explain these things to you and show you the proper procedure for draining capacitors - something that goes beyond where to connect wires. It involves what to wear, how to stand, what to do and what not to do.If I go any further I run the risk of a major misunderstanding, which could lead to you being physically harmed, which I do not want and do not want to be held responsible for.Please understand I'm not being a jerk, just watching out for your and my well-being. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 19, 2009 Members Share Posted November 19, 2009 Verne,Totally understand. In fact, I kind of knew this is where you were going to come back... But I tried as a last resort.I did a ton of research and did find some useful info on youtube etc, but I agree, getting someone to show you in PERSON is the way to go. I'll try to find someone to do that.Thanks for all your help so far!!! Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 20, 2009 Members Share Posted November 20, 2009 OK, here she is! Just need the Marshall Logos on it (LOL) and it is ready to go. I only have 1x12" Celestion Greenback, and no mods -- sounds terrific!!! The other Celestion GH30 is going in next week.I can't tell you how nice it is to have this full size half stack and a 5W head driving it. Perfect for basement/house play volumes, and a ton of satisfaction from the look/feel/sound of it all! Link to comment Share on other sites More sharing options...
Members Verne Andru Posted November 20, 2009 Author Members Share Posted November 20, 2009 Wow! That came out really well. Very well done! Who did the cabinetry? BTW - you could have rotated the on/off toggle so it would orient UP for on. No biggie. If you have a high-school with an electronics shop close by, you may be able to talk a teacher into giving you a quick lesson on how to handle high-voltage electronics. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 20, 2009 Members Share Posted November 20, 2009 Verne: It was done by Sourmash Cabs:http://shop.sourmashguitarcabs.com/ They build heads and ext cabinets at custom sizes. They only got the height dimension wrong for some odd reason... an extra inch taller. Which makes the horizontal splitting line rather odd at that location. No biggie. The cutouts were a perfect fit dimensionally, everything looks stock. The toggle switch on Marshall heads like the JTM45 are actually ON in the Down position, just like I set it here. Matter of fact, you cannot easily rotate the switch anyway, because it is notched for a single orientation! Lucky me, huh? Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 22, 2009 Members Share Posted November 22, 2009 Verne:I snipped C9 and C12 today. I did one leg of each only, in case I wanted to solder back in.In any case, what is the expected behavior of the Tone knob after the mod? Reason I ask is that I was *hoping* this would make the tone knob act as any other amp such that: Left is darker, right is brighter.However, both before and after the mod, I experience the same overall behavior on the V8 tone knob: Left is dark, right is dark, and middle (12 o'clock) is bright. Not good. Originally Posted by Verne Andru I decided to pop the leg on one side of the cap to see what effect it has on the tone. Surprise, surprise - that little bugger is the cause of some major nastiness. The tone control on the V8 works so in the middle you get full treble, turn left and you add bass and turn right and you alter the mid-range [in a good way] but muddy up the signal at the same time.It turns out the "honky" mid-range that adds a "boxiness" to the tone is coming from C12! By simply removing that cap you re-voice the amp in a very good way. The tone pot now does the same thing turning right or left, except it isn't affecting the mid-range because the cause of the midrange problem, C12, is no longer in the circuit.If you do nothing else to your V8, remove C12 and C9. These can be easily snipped off without taking the amp apart. Thank me later. Link to comment Share on other sites More sharing options...
Members gnolivos Posted November 22, 2009 Members Share Posted November 22, 2009 By the way, finished the cabinet off today with the logos. It's no Marshall, but who cares. I love the way these old style JTM45 cabinets look Click here for PhotoBucket pics:Album Link to comment Share on other sites More sharing options...
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