| Author | Message | ||
     mark burgess |
HiI have just purchased a 1x12 combo in very good condition for what would seem to be a good price of £220. I thought the amp was loud when i tried it in the sellers house but having tried it at a jam night on Friday it would seem its a bit on the not so loud side when compared to my friends 65 watt fender tranny cobo he was using. He had the master on about a 5-6 and i was on 8.5 on the gain and 10 on the master and quite frankly not loud enough to be heard with the band in a small venue.With the clean soud anything above on the gain It was breaking up. It has EL34's in it and i am wondering if they need changing? i looked at the manual on the site and it says they are easy to replace but does the amp need rebiasing or is that for models before the rp 100? If anyone has any info on this amp i would be very greatful for it.I am very pleased with the amp tone but to get any push out of it i also seem to need to push the deep and bright switched in is this normal ? sorry for all the questions but i thought i would ask the users on here who know much more than i about these great amps. Also i live in the north west of england in Warrington does anybody know a good tech round here familiar with MM amps?. If i can suss it out i will post a pic on here as i cant see another one anywhere else.  | ||
| Steve Kennedy (admin) |
An apparent lack of power can be attributed to weak output tubes, dried-out electrolytic capacitors or both. After 25-30 years, nearly all tube amps need a "freshening" up of their electrolytic capacitors! I have an HD-130 head that should develop 130 watts RMS in the high-power position, but can only seem to manage about 78 watts. It just doesn't have the "oomph" it should, and sounds a bit thin and lifeless. It is scheduled for a complete going-over when I can get the time to do it! Your amp may be in a similar condition. Try new tubes (without rebiasing) and see if it makes any difference. If the improvement isn't dramatic then it probably needs a "cap job" and rebiasing the tubes should wait until the rest of the amp is in good shape. Steve | ||
| mark burgess |
steve no where on the site can i see a rp 100 with el 34 but i have sussed that this is older model from looking at the site .There is no record inside the chasis to tell me whats right or not should it have the 6l6's in it ? Would a local tech be able to tell me what i need if he has a look. mark mark | ||
| Steve Kennedy (admin) |
Sorry I missed that... the 100 series RP models were originally equipped with 6L6 output tubes (or 5881). The older 65-series RP models came with 6CA7/EL34 output tubes. Perhaps this could be related to your apparent power levels, especially if your amp is factory stock and not modified for EL34s. While EL34s usually work when plugged into an amp designed for 6L6 tubes, the circuit is not optimized or biased for these tubes. Just as a note, you can't assume that the reverse is true... you can't take a 6L6 and substitute for an EL34! The most glaring difference is in the heater current. In an amp optimized for EL34 tubes you might fry the heater winding if 6L6 tubes are substituted because they require so much more current! Checking both the RP65 and RP100 schematics against your actual amp will reveal which configuration you should have. If you have a RP65 series chassis in an RP100 cabinet that could also explain a lot! Steve | ||
| michael kaus |
Actually, the heater current for a 6L6GC is stated as .9 amps and the heater current for an EL34 type tube is 1.5 amps. You can usually go to a 6L6 type tube IN SOME CASES before you can go the other way. Some amps need to have some alteration done to them to use a EL tube if it's designed for 6L6's and the power supply MUST be capable of the extra heater current. MIke. | ||
| Steve Kennedy (admin) |
Ooops..you're right, I got it BACKWARDS! That's what I get for trying to answer questions from work where I don't have my reference material. Thanks for catching that (it probably isn't the first time that's happened). Also keep in mind that these numbers are PER TUBE, so in a 4-tube output stage there can be as much as 2.5A additional heater current with 6CA7/EL34 over the 6L6. Steve | ||
| michael kaus |
Everybody gets an OOPS. That's the rules. Besides, with as much help as you have given people around here, you are entitled. Thanks for the sight and the knowledge you bring, Steve. We all try to help when we can. I wish there were more people on the sight as it helps to hear from other sick addicted people to these amps. I usually check in every day just to see if anybody has some new pearl of wisdom. Again, Thanks. Mike. | ||
| Carl AUS |
Mike I check it every day too! However I'm not as technically minded - but certainly scickly addicted. Peace Carl AUS |