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dlb

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About dlb

  • Birthday 01/19/2022

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    Newport,NH,UNITED STATES
  1. Hello Myles, I posted about tube configuration for my Fender Prosonic Combo. Per your recommendation, I bought a jan GE 5751 and I also had a few GT 12AT7's then I got a pair of Svetlana 6L6GC's. After a few hours of swaping V1,V2,V3 around I think I have a combination that satisfies me. It took a combination of AX,AT,5751 to get there but it's there. My last question on this amp is, is there a big bias difference going from 5881's to 6L6GC's? Thanks a million again!....(Bows low only looking at the kings feet and retreats backwards)
  2. Myles, Before I ask another off the wall question, I feel like I owe a bit of gratitude to your generousity. Knowing you are probably too humble to accept any form of barter, do you have a favorite institution or charity I could donate to on your behalf? (struggling musicians pipe down!) Here goes.... I have an old Allied, Microphone-Instrument amplifier I picked up with great hopes of making a guitar amp out of it. It is probably 50's vintage. I recognized that it was loaded with a pair Mullard EL34's and 4-5 12a??'s. It has reverb as well. It has a master and 4 input channels all with volume and tone. The transformers are identicle in size to most guitar amps. Fooling around I plugged my guitar into it and connected a 8ohm 12" cab to it. It was obvious the tubes were old but it breaks up to a tone heaven. Do you know of anyone that would take on a challenge like this? Or do you think I'm on crack? I would do the cabinet work but I would need an expert to re-configure the electronics. I was thinking Voodoo may be interested.?? Best Regards, dlb
  3. Myles is certainly the more reliable source for your inquiry but I thought I would lend you my oppinion being a Shiva ownwer. I've had mine for about 8 months now and I feel it has re-inspired my aspirations to be a player. It is very consistant and full of character. It does have the dreaded circuit board plunk dab in the middle of all those quality tubes and transformers but I will add that it too is robust and loaded with industrial quality parts. As far as the chassis, it is like any good amp. You can only go so far before you create a boat anchor. The cabinet is like most as far as joints and material thickness. It is heavy but worth every carry. I have other good amps and still use them so my oppinion is not Bogner skewed. Hope this encourages you.
  4. First off, don't start doing mods to that amp or you will get a lot more noise in the higher gain states. These amps can be noisy enough unless you hand select preamp tubes. Have your bias checked! If the amp is over or under biased, you will get all sorts of grainy nonsense down in the range you mention.... especially if the amp is overbiased and running too cool. These amps already start to breakup very quickly in the preamp stages, as that is what they were designed to do, so it is even more critical to have a good output stage after the preamp stage. I would bet, after looking at a number of these, that with your volume set to 3-4, that there is a lot of crossover notch distortion if you scope the amp. To give you more headroom, you need to have somebody look at your first two preamp tubes to see how much above or below 1.2mA they put out with 250 volts on their plates and a -2v bias. If they are the typical Sovtek/Fender tubes, they are probably putting out more than the spec 1.2mA. The 12AX7 has a gain of about 100, so the difference between 1.2 and 1.3 is pretty dramatic. You need to find a nice 12AX7, perhaps a 12AX7C, that has maybe 1.0mA output. The other thing you can do here is put a JAN 5751 in the V1 position. Some good places to get either the JAN or a bit lower powered 12AX7 are Watford Valves, Tubeworld, and KCA NOS tubes. All those folks have links on my website. They are the only folks that have the equipment to measure the qualities you need AND have the tubes you'd want if you go the NOS route. Then, you need to have your output tubes checked. If they are in a midrange, you'd want them to be at a higher range. Something like, if they are a Groove Tubes 4-5 rating, you'd want them to be a rating of 6-7. Last, your phase inverter, let me know what is currently in there. It is the preamp tube that is closest to the power tubes. Tell me what it says on the tube, what kind it is, and as much as you can tell me about it. This is a critical tube in this amp, especially when you run the amp Class A, as if this is not balanced on the A/B sides, there will be a lot more heat generated than is already done when the amp is in Class A mode. When you have the bias checked, find somebody uses a scope if they also use a bias probe. Many folks use a bias probe incorrectly. They might use charts or manuals that say what the correct reading for a particular amp should be, and this is often a bit off as different amps have different B+ voltages. Folks that are more technically advanced, try to figure out their real B+ voltage bu pulling one of the output tubes and taking a reading of the plate pin. This is going in the right direction, and is easier than taking the amp apart, but also gives a false reading. When one output tube is removed, the voltage changes a LOT in many amps. In one Marshall I work on, a 50 watter, it goes from about 450v to about 415v when both tubes are in the amp. To get the proper B+, ESPECIALLY on a Prosonic, you need to pull the chassis and take the reading off the wired side of the socket with all tubes in the amp. Then you can use a bias probe more effectively. Regards, Ok, I finally got around to this. The rectifier tube is a Chinese 5AR4 GZ34 (Fender on it).It has sovtek 12ax7wa's throughout with exception of the reverb tube. It came with sovtek 5881WXT 6L6 power tubes. I have more recently installed Audio Classic 6L6WGB matched set at a 10 rating. It made a bit of clarity difference but took away some warmth. What do you think my next steps should be? Thanks again!
  5. dlb; I am pretty familar with the Prosonic, but need to know if its the head or the combo, as the combo has a slightly different circuit with reverb. As far as the "gain" channel, you have the options of cascaded gain or not. Which config do you want to change? If its the cascaded gain, that's a bit harder, as when you use one tube to drive another, that are both high gain tubes, things can get out of control very fast. Let me know which amp, and what config you want to tone down, and I will give you a few ideas .... the first of which would be to replace the Fender/Sovtek 12AX7WA in V1 and V2, or at least have them looked at to see if they are too stong for the slots they are in. If you have 7025's in those positions, then we have a few other ideas we can go into. Regards, Thanks for the reply, It is a 2-10 combo in the stock state except for power tubes which I've experimented with. It has the cascading gain. I deally, I would like to achieve more clean head room in channel 1 (past 3 it breaks up quick)and less of the synthetic gain sound on channel 2. I've read of mods to put master volume pots in the reverb slot and moving reverb pot to back of chassis. That interests me. It is a cool amp but hard to harness in a live situation. This little sucker runs hot as well, I have a good PC fan I am going to stick in it.
  6. Myles, First, thanks for the heap of helping you so kindly give. I have a newer Fender Prosonic that I dig because of it's portability but I want to sweeten the gain channel. Are you familiar with it's schematics and can you offer any assistance? Thanks again dude.
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