Decko wrote:Gents, perception is not reality. At least my perception of Mesa. Once I saw what these guys were really about I had to admire the level engineering and heart that went behind their product.
Randall has created some pretty complex designs. Mark 5...button switch pusher. And then simpler designs like the mini...
Then to take this engineering and manufacture stateside...not the trend these days in the US. There is much to be said for that.
So I have a question. Based on popular opinion, PCB boards are not the preferred package for amp purists. I have blindly accepted that mind set because many pro amp builders espouse this belief.
Can someone scientifically explain why point to point, boards with turrets are better? Or is this like capacitors and carbon comp resistors where the values do not dictate the overall tonal mojo.
Danny
Hi Danny
As to PCB versus Circuit Cards (eyelets) versus Turrent Boards, versus Terminal Strips, there are good and bad designs, layouts that are well and poorly designed, etc.
The US Military has used PCBs for quite some time. So has NASA, but not every amp builder uses NASA standards, in fact I think only Soul Tone Amps does in some of their models (the non-turret board versions).
PCBs advantages are consistent results, less variation from unit to unit, ease of assembly (less labor intensive). Ampeg (until Kordon Hull sold the company) used well designed PCBs, Selmer, and other manufacturers, too, until with the rare exception (boutique builders or custom shop edition) almost every production amp from the Big Boys utilizes a PCB. I wouldn't say everyone of these PCBs were well designed.
Although PCBs can be machine stuffed (automated insertion), the types of components and values used for guitar amps do not lend itself to automation. Most Guitar Amp (those I have seen every facility), PCB are stuffed and soldered by hand.
PCB disadvantages: A good many have insufficiently thick traces, not ideal for use unless in heads for professional use (Fenders Hot Rod series have heat related issues when gigged every day, after a few years the traces lift) and often are poorly designed (power traces too close to signal traces). Part spacing in some are cramped. A good tech can repair/mod a PCB and replace a faulty component, but I've seen too many lifted traces (fixing an amp after another "tech") to recommend a novice hobbist to attemp such repairs.
Turret Boards and Terminal Strips are physically the stronger and more reliable method of construction. A friend had his Sampson era Mathcless amp dropped from the tailgate of a truck, and after re-installing the tubes, played his gig with no further mishap. If your circuit design is established, there are advantages to both. The downside is repairs and amp modification is harder and takes longer. Another disadvantage comes with component sizes changes, and lead lengths (too short), but neither are obstacles that cannot be overcome.
Circuit cards (eyelet cards) are the most flexible as to adapting designs and for modification and repair. These are less durable strength wise, and if you use the old paper boards have parasitic capacitances to contend with. The solder connection on the eyelets require more solder (almost solder domes) as the solder at high voltage "magically" disappears over time.
I personally hate working on commercial PCBs in Guitar amps, I think these are more trouble than they're worth. There is a tendacy to cram all the parts closer together than is good electrical design and to use flimsey PCB components (jacks, pots, tube sockets). At least Mesa uses chassis mounted pots (flying leads, but not shielded cable) In attempting to fit more into a smaller space, short cuts or cost cutting comes into play, oscillation, noise, come into play.
If the Tubes were chassis mounted (less real estate on the circuit board-more space for an airy layout, if the pots were chassis mounted (not the micro sized ones usually) and some reliable switchcraft jacks (also chassis mounted) were employed, there might be some potential for a better designed amp. However, shielded cables for the preamp and labor costs wouldn't be tolerated the bean counters at Fender, Marshall, and Peavy. Mesa
I would say that for the beginner who isn't building a Betty Crocker (5F6-A, Turret board from Hoffman, etc) that either the turret or eyelet board is a path to a better built amp if you keep the space between components as large as practical.
I have some respect for what Mesa has accomplished and still manufacturing in the US, and not to be a troll,,,,
The early Dual Rectifiers preamp gain channel were exactly the same preamp as Soldanos SLO, right down to the component values.
Any patent attorney with knowledge of the RCA tube manual would state that RS has a few Public domain circuits which he went and patented and the USPTO in their greed and ignorance granted patents.
Minor comments, Mesa warranty requires the use of Mesa tubes, and the inside of the older Mesas I've seen require a resistor change rather than adjust a pot to set the bias every time you change the power tubes.
As to older capacitors, their physical size required larger spacing, which reduces some issues of circuit design. Carbon Composition components have been discussed enough on this and other forums; when used in a few critical positions and properly prepared (baked and then coated) carbon comps resistors can be used to advantage, however, one has to find old school designs such as RCD or Arcol which have the same coefficient of distortion numbers as the old Allen Bradley resistors, and not the low distortion numbers that Xicon produces.
Carbon Comp resistors and the older, larger Capacitors won't improve a poorly designed or poorly executed amp.
Best Regards,
Steve
PS My 1959 integrated amp sounds great with its original components. An updated, recapped (signal) and with new metal film resistors of the same amp owned by a friend gets blown away by my original stock amp to their embarrassment. I would attribute his amps harsh sound to the polypropolene capacitors. I have suggested he replace these with wax paper and foil.
